Either Ice or Water. :)

Definitely Water!

I love me some dragons.

Psychic is my favorite type, but I also love ghost as well.

they have almost the best defenses.

Dark, as long as I am aloud to have at least 1 water type. I am only say dark because:
1) There are no Dark type gym leaders yet... lol
2) My fav non-dragon type ledgendary is a dark type, obviously Darkrai
3) I always wear darker colors, just check out the pics on my profile
My pokemon would be shiny Umbreon (Because I think it looks better with blue), Zorua or Zoroark, and Absol... but I don't feel comfortable with only three pokemon so I would probably also have a Hydregion.
If I didn't have dark types then I would probably use dragon types, and my pokemon would be a Haxurous, Hydregion and a Garchomp... but since I don't feel comfortable with only three pokemon I would most likely also have a Dragonair. I know, I just like more company.
Sammurott FTW lol. Sorry bout the seriously long post.

or water

if im the water type gym leader i would have:
lanturn
quagsire
jellicent (male)

or
electric pokemon:
mareep
tynamo
stunfisk

My Pokemon for my dark gym will be:
Salbye (without the ability stall)
The last evolution of Chespin
Sharpedo
Umbreon
Crawdaunt
Hydreigon

I'd like flying, but Grass and Normal is pretty cool too

Pokemon:

Flying
Altaria
Masquerain
Maybe Beautifly

Grass
Leafeon (Eevees are awesome!)
Lilligant
A un-evolving Bulbasaur or Ivysaur

Normal
Skitty (Kawaii!!)
Eevee (Kawaii!)
Cinccino (Kawaii!)

Either Psychic, Fairy, or Mega.

I might also have fire, but I would like to have ghost more.