I played back in Junior high and High school, then again between a year or two ago. I still enjoy the game, but I can't afford to buy new decks.
I tend to like cards that cost very little to play.
My favorite deck is a Black/Green agro deck made up of mostly 1 cost cards and cheap infect creatures. It's designed with a turn 2-4 victory in mind. If I don't win by then I'll probably lose.
I've also got a greatt deck using Questt for the Holy relic and some 0 cost creatures. I can't necessarily win on turn one, but with the right opening hand I can't lose.
My burn deck uses Pyromancer's Ascention, Iscocron Scepter and Chandra to abuse red cards costing 1-2 mana.
For multiplayer I have a few decks, but the one I really like is my grave pact deck.
I'm working on a new multiplayer deck to abuse Urza's Armor which prevents me from taking any damage from last laugh. I build a bunch of tokens, then kill one off. Last laugh clears the board and kills off every player except me thanks to Urza's Armor. Quite possibly the best idea I've ever had, assuming I can find a way to quickly generate the necessary tokens.