I have a Century WASR 10-63, a Century M70AB2, and had a Century Tantal. All 3 have been great guns. The Tantal didn't keyhole, the WASR is straight, and the Yugo is just awesome. I have also had a MAK-90, and my favorite AK hands down is my milled Arsenal SAM7R-61/SLR101. The WASR is just as accurate as the 1K+ Arsenal. Century makes some decent guns, just look it over first. See if the seller/vendor whatever will let you insert a mag into the magwell and see if it wobbles too much. Also, check for a misaligned gas block and crooked sights!
My AKs in order of how I liked them:
1) Arsenal-hard to beat quality, smooth(yeah I know right? In an AK??), accurate.
2) Yugo M70-solid folding stock, thicker receiver, takes any mag without hassle.
3) MAK-90-Chinese make great AKs. Trust Turkeydad on this: he knows his Polys.
4) WASR-cheap, but reliable and accurate. Never had one problem.
5) Polish Tantal-Didn't shoot it much, but it grouped well and it didn't keyhole.
I love AKs.