The XT is old school. The Citori was originally released in 1973. Mechanically, it has changed very little over that time. The XT is a Trap model, has wood to match that purpose along with a slightly higher rib.
The Cynergy is the new kid on the block. Introduced in 2004, it is a completely new design. Many have said that it's a copy of this or that, but none of those models mentioned are similar to the Cynergy. The triggers are new, the receiver is new, and the wood design is new.
I have almost 10K rounds through mine, and I love it still. I have owned both. When it came time to sell one, I kept the Cynergy and sold the XT.
Both are great guns, the only question is, do you want old or new?