I technically like every Kanto pokemon, but the ones that come to mind most:
#1 - Dragonite: Of course this would be my number one, it's my all-time favourite pokemon! I love it for many reasons, and when I have one on my team it's always turns out to be my best pokemon.
#2 - Meowth/Persian: Meowth was always my childhood favourite, firstly because I love cats and secondly I loved Team Rocket from the anime. I also used a Persian in Soulsilver, and it was one of the most powerful members of my team.
#3 - Blastoise: Another childhood favourite of mine. Not much else to tell, I just really love it's design.
#4 - Flareon: I've used Flareon plenty throughout different playthroughs of pokemon, and each time I use it I love it even more. I'm proud to say Flareon is by far my favourite eeveelution.
#5 - Slowpoke/Slowbro: I just love the Slowpoke line and their dopey appearance. I also love Slowking, as well. Usually I don't like to use slower pokemon in my playthroughs, but for the Slow-line I'd always add an exception.
#6 - Nidoqueen: This was tied with Kangaskhan, but I decided Nidoqueen. I like her appearance and I've used her plenty of times to say she's really powerful. You can say Nidoking is more powerful but meh, I like Nidoqueen more.