For front men, it's all about size and weight. Something to the effect of the Freestlye, Speed 05, Shocker (before 03, who'da thought we'd be speaking of the Shocker as a small, lightweight frontman's marker
), something to that effect. Backmen aren't so concerned with size and weight as their bunkers are generally larger and they do less sprinting, diving, etc,. Their main concern is speed and accuracy, and they lean towards very fast, LP markers, like the A4 Fly, Matrix, Ego, timmy, whathaveyou. Basically any modern electro will suit players in about any position, but front men may be more concerned with having something small and light.