I feel I may have a better answer for this thread after reading the comments.
(Keep in mind, I'm just giving my opinion based on what I have observed over the years. There is no right or wrong answer. Everyone is different.)
GENERALLY, I've noticed gay guys wear desginer trunks (skimpy boxer briefs) and briefs. No Hanes/FTL white briefs.
Older straight men and younger "country boys" are mostly the ones who wear Hanes/FTL white brifs. Sometimes Hispanic construction workers too.
Now as for straight men, generally boxers, and boxer briefs. Generally Hanes or FTL. It's easy to tell a guy who wants to impress the ladies (or his gf buys his underwear... Or finds himself really sexy.) because they wear desginer boxer briefs.
Black straight guys (I am a black man. Calm down.) are really into Polo Ralph Lauren boxer briefs/boxers I'm guessing because rappers wear them. I don't know.
Then, there's American Eagle. I've noticed straight and guy guys wearing American Eagle boxers and boxer briefs. Generally, the boxer briefs are more of a gay thing.
Personally, I am bi, and I wear Hanes and Fruit of the Loom boxers, Hanes, Fruit of the Loom, and Jockey boxer briefs. I may have something outside of that, but generally that's it.
As far as what I find attractive, generally anything other than non-desginer boxers and boxer briefs are a turn off. Desginer under just seems to... Well, gay. The straight guys I know who so wear desginer underwear normally are really full of themselves.
As far as briefs go (any briefs) white ones make me think of children, and older out-of-shape men. Neither of which I find sexy.
All that being said, I've seen guys who make Calvins look really sexy, and guys who make white briefs look sexier than hell. But, most of the time, it's a turn off.
Keep in mind, this is just my opinion from what I observe.