I think people often get caught up with who the best player is RIGHT NOW on a week to week basis compared to all time achievements, status within their team, influence on games, etc.
Drogba is a great striker one of the most respected in the world but he can sit down and be replaced and Chelsea will still look like Chelsea (a very boring squad to watch IMO and this is coming fro ma Serie A fan, lmao). Diego Milito is one of the most dangerous strikers in the world, but when he's hurt Eto'o and Balotelli will go on scoring goals just fine.
I think now that half the season is over you have to add Ibrahimovic into the equation for best active player. I hate Ibra, imo he's a mercenary and will play for wherever they will pay him most, which in some sports may be OK but its not in soccer. But he is a game changer. You need an example, you don't need to look far (this seasons el classico) he came on, scored a goal within what, ten minutes? And a great goal at that. You need another example? Inter Milan 4 - 3 Atalanta. Youtube it.
I think you also need to add Cesc Fabregas into the equation. His stats are ridiculous this season, 12 assists in 16 games or somethin like that, scored two great goals over the weekend, an overall class act.
IMO the greatest player will never be an out and out striker because out and out strikers are fed by good midfielders.
Fabregas, Messi, Ronaldo are the top 3 in the world although Ronaldo is fading fast. A lot can happen until the end of the season, however.