There are advantages and disadvantages both, but its mostly personal preference.
Friends with benefits are good if you just like flings now and then, not always being with the same girl and stuff like that. **** can get really mixed up if one person gets attached and the other isn't, and you have to tread softly because you can do a lot of damage to your rep with girls, but guys will think ur a pimp.
LTR's are decent for your reputation with girls, but if you're really looking for the someones respect this isnt always the path to walk unless the girl is really hot. If you get tired of being single and get attached to friends with benefits', then LTR's are probably better off.
I like both equally but I don't mix them at the sametime. I just got done with a LTR right after xmas that lasted about 5 months and now I'm hookin up tryin to find someone I fancy enough to begin another LTR.