Fast surface / balls, etc = Safin by a mile
Slow surface / balls, etc = Nadal by a mile
I'm currently watching the Safin / Agassi AO SF 2004. That was a great match.
Actually, peak Safin on a slow hardcourt would still be a great match up against Nadal. His movement was superb especially for his height and we all know his ferocious backhand which Djokovic plays to perfection against Nadal. That along with a very blistering forehand and much better serve than Djokovic, I think he could of had a good record against Nadal in general, not just on hardcourts slow or fast. Sure, you can say Safin was a mental nutcase, but he has played plenty of matches which showed his true mental strength.