I would favor Savon over both in amateur fights but if they ever would have meet as pro's I would have a tough time seeing Savon beating either. Savon's strength was always his speed, footwork and workrate which obviously serves the Cuban fighters well in the amateurs as they are groomed for those type of fights. The pro game is another animal for sure.
It's hard to compare amateur and pro versions. I think Wlad was a more finished product earlier than Lewis, even though Lewis ended up with the better pro resume. That said Savon lost to Chagaev and Solis iirc who I don't see giving either Lewis or Wlad trouble.
Both of those losses were towards the end of his career and are fighters that he had beaten. I agree it's difficult to compare amateurs to pro's. It's all speculation.
Felix Savon didn't fight in the same division as Wlad and Lewis. Savon was a heavyweight (in the pros he'd have been a cruiserweight). Wlad and Lewis were fighting at super heavyweight in their late teens. Henry Tillman and Ray Mercer were the heavyweight gold medal winners the years Lewis fought in the Olympics (1984 and 1988). Lewis competed as a super heavyweight in both. Savon won the gold at heavyweight in the Olympics the year Wlad won the Super Heavyweight gold (1996). Wlad and Lewis were so young in the amateurs, I imagine they'd have been blown out by Savon, who was a grown man during his Olympic years.