Pick whatever you enjoy. Both have positives and negatives, and if you're playing for damage then neither class is optimal(So you should pick something else). This question has been asked time and time again, for any amount of classes, and it basically boils down to what YOU want; nobody telling you a bunch of random things about either class will convince you unless you have specific questions.
This is like asking "What's better, ice-cream or cake?". Sure, you'll get a bunch of answers from personal experience, and maybe a bit of objective nutritional facts listed... but in the end, nobody can tell you what you're going to enjoy more, and expecting any different result is both very lazy and incredibly foolish.
@nayeff Funding doesn't make sense. Both Shades and Buccaneers use the same gear in pretty much every slot, so your factors are essentially "Which class has higher damage output at high funding levels?" and "How durable/survivable is my class?". Buccaneers apparently win in the former, although I don't buy it because those damage charts tend to assume ideal situations(Punching bag bosses), which simply isn't the case in most bosses that are worth doing.
For being durable/survivable, I'd say Shade wins hands down. They have superior mobility, more consistent regeneration and they have a Bind(Which is both amazing for parties if you ever get one, to a point that your damage blows Buccaneers out of the water, even if Speed Infusion was actually useful).
That being said, the VAST majority of people who don't enjoy playing a class will eventually quit it. I've known several people who played a Buccaneer, went to a Shade when it came out and then migrated to other classes they enjoyed; if you HATE playing a class, you aren't going to suddenly enjoy them at high-tier content. Unless your ONLY goal is to play high-tier content(Which most classes, if not all, are capable of; their success rate just varies and some put in little effort to get success), then pick the class you like. And even if your only goal is high-tier content, pick the class you like because playing a 'good' class that you dislike will eventually lead you to quit or change classes.
Basically, you're asking "Is Shade or Buccaneer better for bossing?", when neither are the BEST choice. Ergo, you don't care enough about the best choice to want to play it, and both Shade/Buccaneer CAN do bosses(Although one has an easier time than the other). So pick the class you enjoy playing, because you clearly don't care enough about efficiency to make the current top damage class(Whatever the flavor of the patch is) or a class that tends to be high-tier on a consistent basis(Such as Bowmasters, who have never been 'bad' at bossing).