*Scratches his head* I haven't really participated, but the ordinary Troopers seem like the most logical bet... Five of them with a relatively steady hand and good accuracy...? I somehow imagine that most infected won't be able to handle a laser through the skull... And if these guys are as good as their Bio mentioned then they could easily keep up with most infected and fire at them as they run, or even better: the run and gun tactic, where they just stay out of the infected way an shoot them.