I recently just started building with the gatecrash cards and some of them work pretty damn well with the older guild orientated cards. I just started building a House Dimir deck and the new Cipher effect goes really well with some of the old Ravnica sets dimir unblockables, like Dimir Infiltrator and Dimir House Guard (which has Fear which pretty much unblockable anyway).
It's not my best deck by far but it's so much fun when I get Consuming Aberration or Szadek on the field to play with.
I'd probably say that my best deck is my vampire deck. It was my first deck and it just kept getting better and better. I'm about three or four cards off from it being perfect, but unforunatly those cards cost about £5-£10 each and screw paying that much when my deck already kicks butt.
I'm only really missing a bloodline keeper and a few other cards that give other vampires +1/+1 but apart from that this is my perfect deck <3