Statistics try to find out in the club's site. Here is my brief opinion of them:
Pavel Horváth: Consistent midfielder that rarely loses a ball. Prefers to play in the centre falling to the left. Left footed player, has great passing and likes to do impredictible things with the ball. Fast and nice dribbler. He is not an attacking or a defensive midfielder - he is just a Midfielder... It's one of the players I like most in Sporting, excellent worker all match.
Mbo Mpenza: Together with former Sporting's left-winger De Francheschi one of the players who helped a lot Sporting winning the Championship and then was benched. Despite playing +- well in the centre, helping the striker (like he did with Acosta sometimes), his true position seems to be the Right-Winger one. Don't ask him to defend. He is a player for attack, top speed and not a great dribbler. Basically, the strengthes are Pace, Strength ( he is physically strong, but hasn't got much stamina for 90 mins ) and Crossing. Also shoots strongly. Useful player at any squad, I think.
Robert Spehar: ("Striker") Strong, slow, heavy. Spent these seasons at Sporting with long term injuries and bench. His luck in Monaco and Verona wasn't better. There isn't much more to say...