Federer is up there with Armstrong, you're right. It's hard to compare them as they're both so dominant. I think it's fair to call it a tie.
They both have the edge over Tiger for sure. In cycling, the Tour is insane. He beat cancer and won it 7 consecutive times. He almost won last year after three years off and coming off an injury.
The other riders can knock him all they want, but last year he raced in the Tour Down Under, the Tour of Ireland, the Milan-Sanremo, Castilla y Leon, and more. He had to pull out of a couple others due to breaking his collarbone in a crash. Then he raced in the Giro d'Italia.
No allegations of doping have been proven.