hello
1. Porygon-Z - well, I like its lore, its stats, and even its design; I remember those times we spent in the Battle Factory annihilating every opponent with Tri attack or Shadow Ball, and there is a theory I've read that makes this Pokémon's concept way more interesting and deep than before.
2. Breloom - first Pokémon I've used in competitive, but also a great partner for the Battle Factory. Had great times pummeling Talonflame or Charizard with a surprise Rock Tomb, or sweeping teams with Mach Punch. also for some reason I think it's cute
3. Torterra - first starter ever! We overcame every challenge in Pokémon Platinum through sheer level advantage and no strategy at all. And then I transferred a different Torterra in Black 2 to continue his Legacy.
4. Giratina - favourite legendary and first one I've caught. Its encounter in the Distortion World and the previous buildup are just great, and its theme is one of my favourites.
5. Samurott - I actually own two of these, one for White and one for Black 2... it's definitely my favourite Unova starter. It's also of my favourite type, Water!
6. Gengar - Battle Factory buddy... also great in competitive (I can obliterate those annoying Clefables!). If that wasn't enough, it got also a Über-tier mega evolution!
7. Terrakion - another legendary I've used as a party member (though I didn't really feel bad because it was in the OU tier). He's currently my highest leveled Pokémon, with a sky-high Attack and very nice Speed.
8. Zorua - Well, one of the first Pokémon films I've watched, and I've rather enjoyed, was "Zoroark, master of illusion". It's also a fun (although a bit tricky) Pokémon to use in battles thanks to it's ability.
I could have put Zoroark in the list but I decided to go for Zorua because of... well...
(it's an italian video)
9. Scizor - Yet another Battle Factory friend. I used Swords Dance one or two times and then spam Bullet Punch to damage heavily almost every enemy Pokémon. Also, it probably goes without saying, but I've liked its design and this Pokémon in general for a very long time (also because of the Anime).
10. Darkrai - This guy is here mainly because of the movie, some anime Episodes I watched, Pokémon Desolation, and because I used it in competitive... all of these things make it my second favourite legendary.
Also, here are some Pokémon that couldn't make the list: Typhlosion, Sceptile, Manaphy, Honchkrow, Leavanny, Milotic, Hydreigon, Staraptor, Gardevoir...
why did I even bother with the honorable mentions again?