Favourite: its really hard to choose, Gen VI has so many good Pokemon to choose from. If im going to choose design wise there is just one Pokemon that stands out to me: Flabébé. Not a strong Pokemon, but its design is really original and well worked out. The first time I saw it, I knew I wanted it. To bad its such a common Pokemon (especially on WT) I think most people saw it to much and just don't find it that interesting anymore.
Least favourite: Diggersby. It looks like a baby in a high chair eating chocolate. And that cry...
Haven't played X/Y (I AM POOR, DO NOT HAVE 3DS), these are just my impressions based on design.
Favorite: Goomy. The cutest damn thing. I mean, considering Gulpin and Swalot are among my favorites. It hits the sweet spot of what I like, as what I like is apparently little blob things with silly eyes. (runner-ups: Honedge/Doublade/Aegislash for being Ghost Swords, Hawlucha for being a Luchador Bird, Klefki because I love Pokemon everyone hates and also it's an insane concept, Male Meowstic, Barbaracle because I am a gigantic contrarian, Tyrunt/Tyrantrum because T-REX bang a gong get it on, Skiddo/Gogoat, Slurpuff because it looks as profoundly dumb as Bibarel, Trevenant, Pumpkaboo/Gourgeist)
Least favorite: Sylveon. ITS RIBBONS ARE FLESH. Also it has the creepiest eyes. the creepiest. *shudder* (Runner-ups: Binacle, Aromatisse, Heliolisk, Yveltal, Zygarde, Diancie, Female Meowstic, Furfrou, Scatterbug/Spewpa, Clawitzer, Florges, Braixen/Delphox)
Of all of the gen. 6 Pokemon, my favorite is Greninja. I think it looks really cool and I found it very useful for battles. In fact, I would put Greninja in my top ten favorite Pokemon. With how many Pokemon exist, that's one of the highest compliments I can give to a Pokemon.
My least favorite gen. 6 Pokemon...I don't really know. Nothing really stood out as "oh, I dislike it so much, it's one of my least favorites". So, nothing to say here (until, I find out that I truly dislike a particular Pokemon).
Oh my, that's so hard, I have TWO favorites: Fletchling and Sylveon. They are some of the top cutest Pokemon ever created. I think Fletchling is the cutest of all bird Pokemon by a wide margin, in fact.
I think my least favorite would be the Binacle line. Just can't get past the ugliness.
My personal favorite Gen 6 Pokémon would have be Aurorus, because it combines two things I love: Dinosaurs and winter (not to mention that it's really majestic).
As for least favorite, Diggersby, because that thing is one of the ugliest Pokémon in existence imo.
Favorite: Talonflame just barely edges out Sylveon and Meowstic. It was nice to have a flying type in my team that I could use in battle on a regular basis for once. Plus, it's based on my favorite bird.
Least favorite: Aegislash simply because it keeps kicking my ass on wi-fi battles.
Time to tackle the, for me, hard task of choosing a favourite... ;D I think I'll have to pick more than one, with Aromatisse (does anyone else like it? I see so much hate for it lol), Noivern, Goodra, Dragalge and Malamar being my favs :3
As for least favourites, I'll have to say Slurpuff, Hawlucha, Dedenne, Trevenant and Avalugg. For the latter two, I was really expecting cuter evolutions and Phantump especially doesn't make sense to me how it goes from cute, Casperesque tree ghost to that... Evil-looking creeper tree. XD
Oooh, to hard of a decision...XD. But If i had to say my favorite Kalos Pokemon would have to be my baby: Yveltal (honorable mentions: Xerneas, and Gourgeist as well xD) I just love that high flying dark bird of mass destruction and doom. o3o. <333
My least favorite Kalos pokemon? That's easy: Klefki. That thing drives me nuts. Never will use that Pokemon in a million years.