There are many ways one can based their top 10 best players' list. You can do it through tournament wins, placing high in major tournaments, prize money earned, consistency from beta to now, overall skill level, mentions by other pro players, etc.
Once you list your top 10 best players' list, you should give your reasoning, so people can see where you are coming.
I'll start off with mine.
My list is influenced by the player's environment. GSL is the best league/tournament where the topmost caliber of players participate, while the Korean server has the highest skill level. So naturally, most of the best players would come from the GSL.
IMMvp: Most recent season GSL championship; shown top-level play in team leagues
oGsMC: Previous GSL champion; consistently shown high level play throughout the GSL seasons.
IMNestea: Previous GSL champion; placed in the top 4 in the GSL at least two times
MarineKingPrime: Took second place twice in the GSL
Jinro: Finished in the top 4 in back to back GSL seasons
oGsTop: First Code A champion. Did well in the first season of GSL until losing a very close game to fruitdealer.
Idra: Has appeared in all 4 GSL seasons. Shown consistency, improvement in skill level, and tournament rankings.
Fruitdealer: Previous GSL champion. Fortunes have somewhat declined from GSL 1.
TLO: Shown he can compete with the best players in the world by qualifying and advancing in GSL 1+2. Consistent high level play from beta to now.
Huk: Had two accounts in the Korea ladder in the top 10. After 4 days in Europe, he has managed to become the number 1 player with 4k points.
Edit- I'll add up the tallies from people's entries to see what the general consensus is. I'll use a 10 point system (1st=10, 2nd=9, etc). Also, I will only consider lists that have all 10 players and is serious.