My main deck is a sliver deck, which still needs some editing, to find the perfect balance of mana and monsters. When it is successful though, it gets pretty insane.
"Now I play Winged Sliver so now... all my slivers have flying, +3/+3, can be tapped for mana, have trample, have double-strike, ect."
My secondary deck I made at my first FNM and then added to afterwards. It's a white and artifact deck. Works pretty well but like the sliver deck, I'm trying to find the balance of it.
I'm pretty new to MTG (just started playing a few months ago, and it's been on and off) so my decks could probably use a lot of work.
EDIT: I chose white as my favorite because I enjoy using my white deck more than my Sliver. It's a bit more of a challenge, but at the same time is easier to use. Once I fix it, I think it'll be much better.