Have your preferences changed since Fallout 3 since the introduction of DPS etc?
I liked Laser's before, and only used Plasma for fun; I found it too slow moving for any use other than VATS. Now, I've yet to use either of them, but I've got a 100% Plasma Rifle with Accelerated Velocity mod, a 100% Laser Rifle with scope, beam splitter, and (hopefully you can add 3 mods) the damage increasing mod.
But, the truth is, I've only used That Gun, and This Machine... Same ammo, the reload on the Machine is insanely fast and damage is superb on both. I have a cowboy repeater for backup, and a varmit rifle with night scope for those annoying head shots from 1 click. Truth is, I love the variety.