I have the Tri-beam laser rifle and a Multiplase rifle and i wanna sell one of them but i am not sure on what one is better can someone help me out?

Depends what you are going to fight; however, there is only three multiplas laying on the ground. You may be able to buy them from BoS or Van Graffs, however both of them is likely to be decimated at some point.

Tri-beam is good for anything but Death Claw, while Mulitplas is overkill for anything less than Super Mutant.

Sell them both and put your skill points into Guns.

Ignore the trolls and consider waiting to see how lasers and plasma are each affected by the the soon-to-be-released patch.

Also, I think Tri-Beam Laser Rifles are easier to buy again later, but I could be wrong there.

There are only 5 multiplas rifles in the entire game while there are an unlimited amount of tri beams in the game. I believe the earlier one is the tri beam with the BoS Missing Laser Pistol quest.

Just store weapons you might use in the desk in victors shack.

Of the two weapons the multiplas is more useful by far as laser rifles simply are too weapon and 3 stuck together is still too weak.