Many beginners mistakenly assume that the higher level of a player means he is better than the rest. It’s not quite true. In my opinion the best players (with the exception for the goalkeeper) are the quickest ones. You can recognize them by a red-coloured «Speed» indicator. However the rest of parameters should be considered too, especially «Roughness». It’s recommended to avoid players with high roughness parameter since they’re more inclined to break rules, getting injured or removed from the field. Also it’s not worth to buy players if you have not started playing qualifying matches in one of the championships. Because of low popularity of your team stronger players will ask you to pay them higher salary or will reject to join your team whatsoever.