360 Question

Ok,this is for you guys that have been building / running 360 stuff for awhile. I always had and run 340's, (still have two) but with them both having been bored now I figured I better go ahead and start trying to put a couple of 360 blocks in the bank for future use. My question is, which year block would be the most desireable for casting quality etc. Anything else to look for or be aware of?