I read a few comments in threads on this board and others where people like regular laser rifle better than tri-beam. Could someone explain why this is so?

Less ammo consumption, the ability to have a scope, and the reliable accuracy are what make me like the regular better for me, even though I never use energy weapons. The tri-beam with all the GRA mods is fun to have, but your character better be rich, because the prices for buying the GRA gun and mods stack up pretty high.