I'd say any deck with Stardust Dragon and Stardust Dragon/Assault Mode. I love being able to counter just about any move, and with the right cards, I can get Stardust Dragon/Assault Mode out on the second turn. IRL I run a synchro deck, but it still uses Stardust Dragon and Assault Mode (not as good as my original synchro deck that got stolen).
my flex-deck :P (synchro swarmed the field with no cards on the field and only dandylion, one-for-one and debrisdragon...got shooting star, draco equiste, brionac, one fluffy token and black rose on the field...i got honested and lost :D)
k serious now: anti-meta (currently: D.D. and/or special summon lockdowns/counters and/or anti-synchro) and if your anti-meta-deck depends more on D.D., it's generally tough
besides that: for the moment gusta or gallis-FTK (i prefer gallis, for now)
gusta (or gusta-mindmaster-loop):
gustas are generally awesome, cuz they keep recycle themselves back to your deck, which makes yourself almost invincible against attacks (piercing dmg could be a problem, though) it also benefits with beast- or psychic-type supporting cards (overdrive teleporter ftw) and of course there's the mighty "mindmaster" - gusta-loop = win if well played synchro swarming the field is really easy with that type of deck (even withouth mindmaster...you barely need him to be honest...so it's still a pretty good deck, if the next banlist will be released)
gallis-FTK (or orange-gallis): this deck is surprisingly flexible and needs a good deck-building-skill to be a successor, but once it will come in speed, it will own the main target of this deck is of course FTK (or at least OTK) your enemy, by using gallis, the star beast's effect over and over again (koaki meiru doom ---> genex-ally-birdman ---> gallis ---> finest ownage) and the most powerful part about that: you only need 3 cards for this combo and everyone of them does not have any restrictions (yet) and if you are lucky enough to draw them in the very first turn - win - no exceptions but what will you do, if you won't draw them in the first round/s? cuz we want to get sure to gallis your enemy our deck is now just orange D: !? do not let yourself down! no spell or traps are not automatically your doom! if you are under pressure ---> gorz if you're afraid of traps ---> jinzo put some tuners, quickdraw-dandy, treebornfrog and/or monarchs in there and you will be busy for some time the're also defense/wall monsters and/or searchers/drawers it's just awesome (till the next banlist...)
about the gallis ftk: just saw something AWEsome: instead of koakimeiru doom ---> genex ally birdman ---> gallis, he summoned armageddon knight ---> plaguespreader zombie ---> brionac ---> gallis and looped brionac & gallis half of the guys deck was 10 - 12 star monsters and to have enaugh cards to discard for brionac, he added cards like volcanic shell
together with genexally-koakimeirudoom combo, that deck is now like ownownownownown about 50/50 chance to ftk and with every draw(turn) your chances raises about 8% to OTK..well if your opponent don't decide to counter
There is to many decks that are hard to beat. There is e-hero, blackwing, burn, warrior, dragon, a deck base on a attribute, a lockout deck, lightsworn, a deck that returns cards to the hand, ice barrier, a synchro deck, and many more. It is all about what people want to use.
you got two choose kill yourself or kill yourself what are you going to pick and if u don't like me that too damn bad because i don't give a fudge