Favorite Pokemon Type(s)

Water types, agreeing with many other people up there. X3 Next would be Electric, Grass, and Normal (has the best variety).
Water Team: Politoed, Milotic, Corsola, Swanna, Azurill, Vaporeon
Electric: Ampharos, Raichu, Emolga, Manectric, Zebstrika, Pachirisu
Grass: Lilligant, Whimsicott, Bellossom, Leafeon, Meganium, Tropius
Normal: Delcatty, Eevee, Jigglypuff, Spinda, Chansey, Cleffa

Water types are my absolute favorites. They're well-rounded in both stats and movepools (I love ice attacks but not ice types usually; water types cover that for me) and there are many awesome-looking water types. (Some not so good looking ones too but all types have that problem.)

Plus, my favorite Pokémon of all time is Vaporeon. :3

Water.

Blastoise
Poliwrath
Empleon
Samurott
Golduck
Lapras

My favourite Pokémon is a normal type but I like ice best. Ice has been my favourite since the first time I saw Articuno - before then it was water. <3 Although dragon and fire are rapidly catching up.

Grass, Water, Fighting, Flying, Rock, Dark, and Ice are my favorite types

I find myself unable to choose between Ice and Electric types for my absolute favourite type. Fortunately those two types complement each other in battle exceedingly well. I also tend to heavily favour Bug, Grass, Poison and Normal types.
I think it goes without saying why I loathe Fire-types XD

I would say my favorite types are probably Steel, Psychic, Dark, and Poison.

At this point, it's hard to think of a team, but ones I'd consider are probably Aggron, Magnezone, Slowking, Reiunculus, Alakazam, Gallade, Umbreon, Scrafty, Weavile, Toxicroak, Vileplume, and others I can't currently think of.

I favour a few and voted for a few, but I mainly deal in Dragon and Water types. I have found them to be the most useful in my experience of competitive battling. I use Dragon types for their raw offensive power and usually wide move pools.

And I use Water types for their natural bulk and specially offensive capabilities. I use other types like Ghost and Psychic types for their tricky tactics and again offensive capability.

I should also mention the necessity of a Steel type, as I always have one Steel type on my teams for their defences and naturally high amount of resistances to other types.

I had chosen Ghost, Grass and Poison. All of them has a modest interest, so that's good.

I particular love Grass-types because plants have so much potential to base a Pokemon on, and what we have is just the tip of the iceberg. It's little wonder Grass is one of the more populated types every Generation. Their status moves are very useful for causing some disruption on the opponent, especially Leech Seed and Sleep Powder.

Ghost is great because it's a rare type that not many Pokemon belong to, and they are particularly useful as a type, with two immunities and not many weaknesses. I like that each Ghost-type possess a unique attribute that can differentiate their roles from one another.

Poison I chose because it is a useful defensive type and some of the Pokemon are quirky. Again, there is some potential for new Poison-types, although this had not been the case these years.

Thanks for reading.

Ever since R/S/E and my obsession with Steven Stone, my favorite type has been Steel-type. There are so many cool Steel-type Pokemon, like Lucario, Aggron, Scizor, Empoleon, etc...

So my top three favorites are...
Steel
Ice
Ghost

Personally I've always loved fire, electric and water types because most of my favourite Pokemon have been those types, and just because I love the sort of attacks they can use

Bug, Poison and Steel. Poison-types still don't get the respect they probably don't deserve. Even though it's only super effective against one type (Grass), the Poison type has some of the weirdest and best Pokémon designs in the games. Steel-types are just cool in general, having a good mix of designs and stats, and it's the same story with Bug-types, especially since Gen V gave us some of the best bugs.

Weirdly, though, my favourite Pokémon isn't any of those types.

Psychic

Team:

Mewtwo
Mewtwo
Mewtwo
Mewtwo
*Shiny* Mewtwo
Mewtwo

Fire, Electric and Dragon. They have some of the coolest Pokemon and are just simple to use. XD

My favorite is Dark. As for a team of all-Dark Pokemon... hmm... here's what I've got:

Umbreon
Honchkrow
Tyranitar
Shiftry
Sharpedo
Spiritomb

I'm sure there's a better team than this, but that's what comes to mind at the moment.