Guns are more versatile and easy to use because of their ubiquity. For my second playthrough, however, I decided to try a different playstyle by using energy weapons. I won't lie; for the first half of the game I regretted my choice because of the lack of variety and ammo, but I stuck through it and am pleasantly surprised at how easy the game can be on Very Hard difficulty--hardcoe turned on. This may be partly due to the fact that I have already played through the game but I really do believe that with the right perks and a really high Luck stat, you can kick serious butt.

I'm going to go ahead and put in a modest example of how neat the Laser RCW is (warning: spoiler for Boone's quest): http://www.youtube.com/watch?v=ePpMG2Evbb8 . When playing through this quest in my first playthrough with a Guns-focused character, it took much longer to take out the Legion soldiers at a similar level. Shortly after this I went after the Deathclaws in Quarry Junction and also had an easier time wittling down their health.

Of the guys you mentioned only some of one group use energy weapons. The big blue guys and Spartacus use lead shooters.

I was talking about general ambience, but looking back at your original post I see you were referring to the weapons used by the NPCs. Fair enough.
Nice that the game supports more than one approach.