My family has a large collection of MtG cards, so I've built a bunch of decks over the years, and have made some pretty good ones. However, when playing with my entourage, I usually lose despite my greater experience due to two reasons: firstly, my decks are built for interaction more than win conditions; and secondly, power creep leaves many of my cards underpowered compared to new stuff.
My very first deck was my Goblin deck. It's been editted a couple times, but not much big change. Mostly old cards. It's a fast-acting aggro deck, with a good one-hit kill combo that accounts for half its wins.
Next I have my Beast-Life deck. It's a rather slow deck with mana acceleration. Big creatures, lots of life-gain. Rarely ever win with it, but it has some great stuff that allows me to slowly destroy enemy defenses without losing my beasts. Contains a combo that resets my life total about once a turn.
My signature deck is my Legendary. It's filled with stand-alone powerhouses, direct damage, and the like. Also contains elementals to use while building up to the higher mana costs.
My favourite to use is my Merfolk deck. It uses forced islandwalk, counterspells, mind-control, and a bunch of manipulation cards to mess around with the opponent. It is my most successful deck, because I can just counter or gain control of my enemies' powerful standard stuff.
My last and most recent build is my Lime deck. It uses small amounts of life-gain, decent token generation, and a lot of creature protection. I usually only win when I get my one overpowered mythic leveller out; he wins the game for me.
I also have a tri-colour instant-based deck currently being tested, and a Shadow deck in the works.