Ah, the good old what's-your-favorite-type question. We haven't had a thread like this in a while. I'm just going to make one small note - if you're going to post types, explain why they are your favorite. "Just for the heck of it" is a valid reason in this case, but as long as it's a reason. Just listing types without much of a rationale behind it isn't really something that has a lot of discussion value - and we don't want this thread de-evolving into spam, do we?
Didn't think so.
In a any case. Personally, mine are (in no particular order):
* Grass - Probably my top favorite. I'm quite fond of plants as a whole and I have quite a bit of a thing for symbiotic plant-creatures both in and out of the Pokémon context - and though they tend to have relatively many weaknesses compared to other types, they manage to remain incredibly viable in battle in spite of them (through a diverse arsenal of moves). Like all types, there are many hits and misses in the design department - ranging from ridiculously awesome and creative to just balls with leafy bits sticking out of them. But really, one would expect some species to be more animal than plant and some species to be more plant than animal, some species to be active mobile creatures while others preferring a more sessile life style, only mobilizing to defend themselves, capture prey or reproduce. Diversity is an awesome thing, and Grass-types have quite a bit of it.
Also, Leaf Blade. Frigging Leaf Blade. Your argument is invalid.
* Bug - Let's begin with one statement: Arthropods are more awesome than you. Nevermind the fact they're so damn alien compared to other "common" creatures, they're also the most successful, diverse phylum of animals on this planet by a very large margin. I could spend quite a while gushing about all the reasons they are awesome as hell, but that would be royally off topic. The point is there's a lot of idiots out there who don't give arthropods the respect they deserve and have either been so conditioned by society to dislike them or are insecure and afraid of things that are mostly harmless to them but are still more successful and diverse than they ever could be and thus have to defeat them to prove to their fragile human egoes that they're still OMG THE BEST AROUND - and to these idiots I say "Kindly go and get fire punched by a mantis shrimp". Actually there really should be a water/bug mantis shrimp that can learn fire punch. Trufax.
... Anyway. I like awesome arthropods and that obviously projects to Bug-types. Though initially a rather useless type (ironic, considering Pokémon as a whole started off as a tribute to the bug collection hobby that used to be all the rage in Japan when the series' creator was a youngster), Bug-types have seen a renaissance in the Fourth and Fifth Generation of the games - and now armed with moves like X-Scissor, Bug Buzz and Quiver Dance (along with the classic Gen 2 Megahorn) they can finally kick ass and take names as nature clearly intended. The addition of several amazing species such as Volcarona and Galvantula to the already impressive pool of Things That Will Kick Your Ass like Scyther, Scizor, Heracross and Armaldo only served to make the type more amazing. Because really, nothing says fuck you more than a ginormous moth that commands the power of the mother fucking sun.
* Fighting - Okay, on first glance, 'Fighting' seems like a rather silly type idea as most Pokémon are fighting creatures. But "Fighting" here is a reference to martial artsy stuff - complete with 80s training montages, super secret techniques passed down by ancient Asian masters and species that have either been trained in human-like martial arts... or inspired them and passed them on to humans. I like the latter explanation more actually - especially with so many human martial art styles being based, vaguely, on the movements of animals. I like the idea of different species learning from each other. *shrugs*
Like Bug-types, Fighting-types have been hampered by stereotypes formed by unfortunate early designs/portrayals thereof (witness the Machop line, nearly continuously portrayed as drooling steroid-breathed violent body builder types, poor things) and a lack of a viable move pool in early generations (particularly in Gen 1, where their most powerful natural enemy, Psychic-types, were already overpowered and overrated) - and like them, they've blossomed into something that can quite literally kick your ass into next Tuesday with ridiculous slow-motion Wuxia bullshit that probably means their voices are not synched with their lip movements (although I suspect newer species gave the whole lip synching thing a miss and communicate by waggling their fucknormous eyebrows instead. I am looking at YOU, hitmonmuppets!).
Personally, as far as Fighting-types go, I am heavily biased towards the more creaturey looking ones such as Blaziken, Breloom, Toxicroak, Mienshao and yes, Lucario (even if the poor thing has been mostly ruined by Fanboys, Furries and other things beginning with -EFF!-). However, I can easily see even the more humanoid looking creatures as rather nifty in their own way. Besides - let's face it, guys, this is the type that has a sentient ambulatory potato with slinkies for limbs and angry eyes as one of its earliest representatives. I'm sorry, but in the This-Is-So-Ridiclous-It's-Awesome sweepstakes, Hitmonlee takes the cake and eats it. With its feet. Because it has no mouth. And it must scream WATTAH!
* Dark - I'll admit it - these days, I find myself feeling slightly awkward for liking Dark Types, if only because they are the stock favorite type of every Fangirl and Mary Sue out there, because y'know, they're so "dark" and "mysterious" and "misunderstood" and "goffik" and go cry me a fucking river, Emo Kids. You've just gone and displaced ONE stereotype about Dark Types (They're EVIL spawns of PokéSatan and they thrive on bringing disasters, chaos, hatred, rage and carrot!) in favor of another (THEY'RE THE PERFECT REPRESENTATION OF THE TURMOIL IN MY SOUUUUUUUL IT'S HARD BEING A TEENAGE BRAT. IT'S HARD AND NOBODY UNDERSTANDS. IMMA GO NIGHT SLASH MYSELF.)
Ahem. Now that I've gotten THAT rant out of the way.
Well, the 'misunderstood' thing isn't entirely inaccurate. Most Dark-types (or as they are called in the Japanese version of the games, 'Evil' types) either use manipulative battle tactics such as taunting, intimidation, demoralization, striking from the shadows and what have you - or are based in terms of design on creatures (real or mythological) that inspire fear and loathing in the hearts of many humans. Yeah, really evil there. Until you remember two important factoids:
1) The concept of a 'fair fight' is a fairly human one. Nature is seldom that fair. "Underhanded" battle tactics are fairly universal and some types do it even worse than Dark-types. Psychic-types, for example, manipulate the minds of their foes using illusions or even DIRECTLY without bothering with all the psychological warfare Dark-types do. Double standard, much?
2) Most species that strike terror into the hearts of men are fucking awesome and only got a bad reputation because of cases of mistaken identity by a powerful animal - or more commonly, ignorant idiots who provoked, fed or were simply spooked by an animal that proceeded to either kick their ass or went off on its business as usual, oblivious to the strange hairless primate who then proceeded to run off to his tribe and tell them exaggerated tales of the demon beast he just ran into.
So yeah. You've gotta appreciate intelligent, observant and generally powerful species who can turn the tide of battle by using their brains - and I don't mean by using their brains to mind-control their opponents into punching themselves. The psychic immunity (Perhaps due to being too smart to fall for Psychic Jedi Mind Tricks) and the strength of their tactics against creatures that rely on their mind powers too much by disrupting their discipline/concentration/what have you is also a plus. Until a bug punches them in the face. Because spiders are not in the business of psychoanalysis.
* Dragon - Originally a rare magical "superspecialawesome" type with many resistances and armor-piercing diversity, dragons have since become much more common and generally easier to counter.
Amusingly enough, I'm not fond of most Dragon types - many of them are incredibly generic and some are utterly derp (between The Winged Orange Barney, the Flat Rage Lizard and the Spiky 3-Year-Old-Drawing-Brought-To-life, there is quite a wealth of derp). No, the appeal of this type to me is more the concept of the type itself - I enjoy the idea of these creatures being linked to some sort of ancient, unique form of ancient ambient energy - an unrelenting force (Insert Fus Ro Dah joke here) that can only be defined by itself. Something about that resonates with me - there is a certain "stuff of legends" value to this force, seemingly tapped into at random by seemingly convergent lines (and some species not even of the type) which is both its appeal and its downfall - alas, their rarity and power, as well as their ZOMG DRAGONS!!11!(one) attribute, made them another goddamn Mary Sue favorite - But I've liked the type since very early on and I don't intend to stop liking it because a horde of idiots started liking it. That would be a complete Outrage.