Originally charizard because i was an excitable little shit then empoleon because i thought piplup was the best starter of gen 4 then gardevoir/blaziken when i became a pokephile and now it is set on weavile because my one fell into becoming my main

Mawile! She's so cute and interesting. She was tied for my favorite with Steelix for years, then she got even better when she gained fairy type, then she got really strong with her Mega form. I spent a long time getting a perfect IV+EV lvl 100 Mawile in X&Y.

I prefer the looks of her non-Mega form, but both are great.

Umbreon. No question.

That's really tough, maybe Zoroark, but it depends on my mood. Mewtwo, Mew, Arceus, etc. etc.

Gardevoir obviously x3
close second by goodra

Rockruff, Gardevoir and Mewtwo, since I own OC characters of them respectfully ^^

It used to be Rayquaza when I was a kid, but I only cared about battles.
Now I like the Poke-Snakes like Milotic, Serperior too, but its so hard to decide on a favorite.

There are just too many awesome pokemon >w>

Regular - Ampharos - Hard to say why, looked like a fun little thing in the anime, helpful too.
Legendary - Giratina - Love ghost types, and it's the only ghost legendary (outside of Musharna but I think that's mythical), also looks badass in either form
Mythical - Victini - Did the event early on and kept Victini on my team throughout, it's a cute little shit, that's for sure

Mewtwo, Metagross, Magneton annnnnnnnd Golem also Cofagrigus

Lockpin (mega) and Gardevoir <3

Scolipede and ferrothorn, first one because it's a cool bug with the resting bitch face and an interesting pattern, and the second one is a plant shaped like a ufo/tank, and spikes as well.

Classic, as somebody who saw the first series when was a kid I'll always pick MewTwo.
I have a thing for anything which is dark, mysterious and misunderstood.

Gardevoir and Haunter

Ever since gen 1, i adored sandslash (and while its Alolan variant is "cool", pun pun, i still prefer the original). Even his pre-evolved form Sandshrew looks nice and cute. Maybe it's because liked Sonic as a kid, but even now, the design is simple yet elegant and "sharp" (PUN PUN).

One sit that ranked all your pokemon in terms of face gave me Scizor as number 1 twice, and i gotta agree, that guy, from its sleek design to its bright red coat, is also amazing.

Vaporeon and Jirachi for me. All day, every day.