You pose some interesting questions. However, you have to look at several facets of the game before taking into consideration a new #1 player in the world.
1. Who can beat Nadal on Clay?
This is something that has to be answered from within the clay court season. This time around Canas is going to be seeded and I think Canas or Nalbandian pose the biggest threat to Rafa on Clay.
Novak can play on Clay, but I don't know about Tsonga. Given his slow hard court dominance at the Aussie and Pacific Life Open, this could be a surface where he can also dominate on.
2. Who can be Roger on Grass?
I don't know that anyone can. Rafa had him beat last year in the finals and let it slip away. The Americans (Roddick, Blake, Young, Fish, Queery and Isner) could all give him a run if they got him early in the tourney, but the closer you get to the finals with Roger I think the more likely you are to choke by his name sake at Wimbledon.
Roddick, Fish and Isner all pose the biggest threat as well as Igor Andreev and Karlovic. All of these guys possess the huge serve it takes to win at Wimbledon if you don't have Roger's game. Isner just out of college is my favorite to beat him (Federer), but how much has a college kid played on grass?
If you can answer those two questions, then you may be able to take a look at who really stands a shot at finishing #1 this year. It won't be Tsonga by all accounts, but Novak is good enough on all surfaces and has to be a favorite at the US Open this year.....I think if he can reach the finals at the French and the Semi's at Wimbledon coupled with a great run at the US Open and some of the other hardcourt summer series tournies, then Novak has the best chance to win it all and finish #1 this year.
With the tennis ranking system the way it is, it's hard for players to really say they finished #1.
