See this link for comprehensive information about ammo:
[url]http://www.ammo-oracle.com[/url]
The short story is ... buy whatever is inexpensive for you, easy to obtain, relatively good quality (reliable / accurate), and doesn't leave a bothersome clean-up chore in your rifle after shooting!
Ammo prices vary; what's "best" one week (pricewise) may not be "best" the next week. So if you can afford to buy in bulk, then you can secure yourself an ammo supply that will provide you with consistent performance for awhile.
As Oslow said, Russian stuff (like Wolf) is relatively "dirty". South African military surplus ammo enjoys some popularity with many people on this board ... I haven't shot any of this myself but have heard it can be "dirty" also (but it can be had inexpensively).
Check out ammoman.com and Natchez Shooters supply - both good sources and fair prices. Frequently you'll run across ammo sales at either or both places for some pretty decent stuff.