I'd have to say my Messenger Titanium Pearl. This was my first bowling ball which I got over a year ago. I had mixed reactions with it for about 11 months, and for some reason in the past few weeks, it has just been amazing. I found out as long as I don't play any deeper then third arrow, this ball is a monster. I usually play a huge inside line because of my axis rotation, but my new favorite line to play is a really inside line, almost a straight line with like a 3 or 4 board hook on the backends with my messenger. It recovers really well, and carries amazingly well. There has to be semi-dry backends though for it to be effective, but it's a monster when the condition allows it to be. I have been averaged 25 pins or so ever since I found out how to use this thing right.
Also, another surprise for me so far is my Brunswick Fuze Purple Pearl. I bought it thinking it was going to fit perfectly into my arsenal and be my #1 medium oil ball. I drilled it with a basic label drilling (I'm left handed, so the pin is to the left of my ring finger, with he cg in center grip) and if there is any carry down, it will barely move. Any dry and the thing takes off. It hooks too much when it sees a sign of dry, and too little when there's some oil. That wouldn't be so bad, but the thing is WAAAAY too angular. I am left handed, and almost anytime I hit the pocket perfectly, the ball is coming in at such an angle is hooks to the right of the 8 pin, leaving the 8 pin standing there. Possibly going to get it redrilled with the pin above the bridge and cg in center grip. So far, it has been pretty disappointing.