To be honest, Nadal is the most convincing. Saying as a Fed fan. Nadal just steps up when it mattered, especially to him and rarely loses big important matches against underdogs. Plus he is also able to turn to his favour even if condition says otherwise, like winning slams on his less favourite surfaces.
What are you talking about? First of all, that Nadal is so vulnerable on not just one surface but two... that doesn't exactly spell convincing
to me. Secondly, "important matches"? Since their respective breakthroughs on the top level, Nadal has lost way more slam matches to weak players than Federer has. As for strength across surfaces, Rafa's record in Wimbledon for example 2012+ is fucking embarrassing for an all time great. "Stepping up when it matters" sounds wrong to me, too... Nadal's mental strength was good when he was younger but have you been under a rock for the last 4 years? He can't seem to come through anymore.
If you combine personality factor, level of tennis and versatility, it's Novak Djokovic. The guy has been struggling from the very beginning. His childhood was messed up by a war, his parents were not rich, he was faaar behind two biggest tennis stars. That is why it's incredible who Novak has become over the years.
Novak has an interesting background, but your 3 criteria? Versatility: Federer wins easily. Personality wise: it's personal preference (but for me Fed's hilarious smugness > Novak's attention craving > Rafito's fake humility).
Level of tennis: depends on surface (Rafa on clay, Fed on grass, Novak on... well... Fed has more slams than Novak on Novak's strongest surface, so...)