I don't remember which generic buccaneer you get that everybody else would get other than Ratbeard.
Ratbeard is an ok companion, but does NOT get Relentless, which is a must have to make that companion the top on my list.
Any buccaneer in general is fairly good. Better accuracy and dodge than Privateer, a little greater damage, and a tad bit less health. And Relentless. Which makes buccaneer's absolutely fantastic. They can deal damage like no one else (except swashbucklers) and have great survivability.
If you recruit a buccaneer, if he is able to learn Relentless x2, he is great. If he is able to learn Relentless x2 and another epic, he will be super great.
I know for a fact that Temujin (the horse barbarian from crown shop, and the swashbuckler starting companion) is one of the most powerful buccaneers I know. Mine knows Vengeance Strike, Relentless x2, Flanking, a Critical, and a secondary damage attack. No buccaneer I currently have recruited comes anywhere near to what Temujin or Subodai can do.
If you do look at Temujin for any reason and decide to buy him, do not buy him until you are level 50. That is right. Level 50. That way, Temujin will be even higher than level 50, and you will have an even more powerful companion than the general public will ever be able to have. That actually goes for any companion that you buy. So, keep that in mind.