Monte Barrett was 23-1 when he fought wlad... i think povetkin at this point is better than barrett was then.. that's arguable though
Byrd was his best opponent. Peter probably the most meaningful (had he lost he'd have retired). Haye his biggest victory. Chagaev his best performance. He's very very close to cracking my top ten. Infact I'd probably struggle right now justifying ten guys above him.
Byrd is probably Wlad's best win, he was a good fighter who had a number of good wins to his credit. Guys like Chagaev, Sultan, Peter, etc were all good wins and you might be able to make a case for them but I'd go with Byrd for now. Haye and Chambers, who I'd put in Wlad's top 4-5, aren't done and if they get a few more important wins themselves could become Wlad's best win.
The Chris Byrd fight happened before Vitali fought Lewis! Byrd won the WBO belt from Vitali! The Lewis fight happened in 2003,the Byrd fight was in the year 2000.