As much as I enjoy multi colour decks, I find the deck building restriction of mono-colour much more fulfilling and the decks more fun to play.
Toby: Bracket 2 Blink deck. Fun, but quite slow to get going.
Malcolm: Bracket 4 Proliferate/Extra Turns chaining. Can be a bit of a gamble how the game begins, but it's always fun dropping Omniscience on turn 4 before hand dumping and playing solitaire for 20 minutes to kill the table...assuming they don't just scoop and we play a new game.
Starscream: Bracket 4 Burn. Uses mass card draw to kill the table all at once with cards like Peer Into The Abyss and Necrodominance. Bonus wincon in Gary/Exsanguinate if someone manages to cut my deck in half.
Squee: Bracket 3 Combo. It's basically my Magic version of Exodia...if Exodia had interchangeable arms and legs.
Shigeki: Bracket 3 Mill/Landfall/Enchantress/Green Stompy. Basically a value engine based around Shigeki being an Enchantment Creature that nets you lands. I want to case Shigeki almost as many times in a row as I want to cast Squee.
Omarthis: Bracket 3 +1/+1 Counters/Manifest. Go tall by making Omarthis really big, then kill him to go wide and overwhelm the table.
Niv Mizzet: Bracket 3 Legends Matter. As many 2-colour Legendaries that care about other Legends/Historic permanents while trying to get all 10 colour combinations out for maximum draw/life gain/burn damage.