I must say, despite my bias, that the Premier League is a better and more exciting league overall than La Liga. However, I will admit that due to Real Madrid's and Bercelona's latest acquisitions mean a lot of the best players play their football in Spain. The Premier League still has masses of world class talent, though. More so than anywhere except possibly Spain.
At the moment, I don't think anyone can argue that Wayne Rooney, right now, is one of, if not the best player in the world. I never used to rate Rooney that highly, but he's having an amazing season this term. Messi is probably playing just as well, maybe slightly better in some people's eyes. Rooney has 23 goals, as does Messi. Though Rooney has played 2 more games overall, due to Manchester United's FA Cup exit and Rooney not playing very many times in the Carling Cup mean that Messi has had more chances to score against weaker teams. While the vast majority of Rooney's appearances and goals have come in the Premier League (seven appearances in other competitions with two goals. though against teams like Chelsea and Manchester City).
In regards to overall team contribution then Rooney and Messi must be close again, while if it comes down to goals only, it's going to even closer maybe. If Messi wants to retain his World Player of the Year award, he's likely going to have to near enough equal or better last year's performance. Rooney is doing all he needs to do to be in contention for something like that.
However, Cristiano Ronaldo is being overlooked despite his limited appearances. 16 games play (two as a substitute) with a return of 15 goals is quite extraordinary. If he can play the majority of games he'll be right up there yet again.
Of course, success in competitions with your team is often something that sways the voting, which I don't think is fully correct. If Manchester United can win the Carling Cup, Premier League, and do well in the Champions League, then Rooney has to be one of the favourites. The same goes for Messi and Ronaldo though, if their respective teams can win some trophies that may be what pushes the voting up.