Its all personal preference, I guess. I just don't see the general advantage of having range, when an invisible predator with sketchy animations due to connectivity issues charges at you (incredibley fast) jumps over you and begins to auto-lock and attack you to death.
Perhaps if the marine had a shotgun or an autolock machine gun, he may stand a chance, but i've killed countless marines doing exactly what I just depicted to you. I noticed that there different characters you can choose in the full version. Pehaps there is a marine that starts off with a more versatile gun.
The Marine actually has both of those weapons.

Also, add me to the Steam list: kajjak (LockjawJones in-game)
EDIT:@fallout3newbie: Sprint, sprint, sprint. The motion tracker generally isn't fast enough to detect you, and as long as you're on the ceiling or wall the Marine will be at a severe disadvantage. Stay away from any Marine you know has a shotgun though, because that damned thing 1-hit-kills both Aliens and Predators up close.