In short hidden mode rush deck is the best. But not funny at all, if you want to have a chance against them you have to use a rush deck too and it's quite a boring match.
Tower building decks are powerful too and more funny since you can combine it with some keyword deck.
let's see... I have 5 tower building decks: Ivory tower (holy based), Sapphire tower(mage based), Onyx tower (brigand based), Carbon tower (runic based), Diamond tower (no keyword). they all need a different playstyle; they have all good statistics but Carbon tower. I will probably create a Lapislazuli tower (aqua based).
Another good deck is the one based on Pyramids (Dindon's one is pretty good, mine have 50% victory). I think that it probably needs some nerfing (mainly in wishing lagoon), it has good potential to be overpowered, expecially in short mode.
A really owerful deck in long mode is holy with big rares. I wonder why nobody talks about nerfing fairy.
About beast,yes it's good. my beast deck have a 2:1 wins/loss ratio but I think the one NG Beholder uses is even better.
Mage decks are really funny and quite powerful. I don't use unicorns 'cause I think they're op, but they can give a really good attack power to mages.
There are other interesting decks but the one I love the most is my zero-cost accumulation deck (93 wins 51 losses). really powerful in long mode but usable also in short. absolutely weak in hidden mode. It's weak against Tower building decks but if you draw return to the beginning you are almost invincible since you can clone it with halfing rogue.
If you want to try it.