I've been playing with and against Skaven for quite a while now. I am pretty convinced that they are the best deck at this point, but I would love to be wrong. There are a lot of ways to build the Skaven deck, but this is my best version. There are no Regionals anywhere near me, in case you are wondering...
3 Warpstone Excavation
3 Contested Village
3 Orc/Chaos Alliance
1 Chaos/Dark Elf Alliance
3 Choppa
13 supports
2 We'z Bigga!
3 Seduced by Darkness
3 Pillage
3 Innovation
11 tactics
3 Spider Riders
3 Crooked Teef Goblins
3 Snotling Pump Wagon
3 Lobber Crew
3 Clan Rats
3 Clan Moulder's Elite
2 Rat Ogres
3 Greyseer Thanquol
3 Deathmaster Sniktch
26 units
50 total
If you are allowed sideboards where you are playing, I would include Mob Up! (vs damage prevention decks like bolt throwers, cut the Rat Ogres) and Veteran Sellswords (sub in instead of the Pump Wagons against non-rush).
Ok, so why is this list better than the alternatives? Well, all the Skaven decks will be playing pretty much similar stuff and often the player who draws the most Deathmasters wins it, honestly. But this list gives you a slight edge.
a) Relatively heavy supports mean you don't just lose to sweepers & Flames of the Phoenix. That Chaos/Dark Elf support isn't a typo, it's just the best option as supports go since it gives you a point of Chaos loyalty.
b) Choppa, Spider Riders, Pillage and Lobber Crew are significantly better than the cards you get from Chaos or Dark Elf. Chaos gives you auto-free Seduces and maybe stuff like Firestorm, but nothing too exciting. Dark Elves have more useful stuff - We Need Your Blood, Chillwind and Shades are standouts. Still not as good as the Orc cards though. Lobber Crew and Pillage by turn 2 is backbreaking against many decks.
How to play it: you need 1 hammer in your kingdom and after that all the Clan Rats, supports, etc. go in Quest unless you are drawing 4+ cards a turn. Do not forget to abuse the Rat Ogres ability if you are fortunate enough to have them out at the same time as Clan Rats or Deathmaster. Against most opponents, you want to use Seduce offensively to burn zones - you normally do not want to attack into blockers. Against Chaos Control and Dark Elf Control, your best card is Clan Moulder's Elite. Against Order, your best card is Deathmaster as most Order decks just lose if you can keep him active for a turn or two. You normally only need 1 development for Innovation - but if you are drawing a lot of cards, don't forget to develop somewhere every turn since the extra HP on the zone can win you close games.
If you are not excited about your first and second turn plays looking at your hand, mulligan. Assume you won't draw anything useful when making that decision.
If you can post a list that is >50% against just this deck, you get a (virtual) cookie.