As long as they get along and love each other, I don't really care if they also love each other romantically and/or have sex. I know the question is to pick one, but I don't think I can. It's kind of like asking me if I'd rather have a blond or brunette partner, I know some people care, but I really don't.
What I definitely wouldn't like is for one of them to be in love with the other, but it not being reciprocated.
So far, I've only ever been with straight guys, so the triad option hasn't actually been an option. I have to admit I would enjoy it happening just so I've experienced both, but you can't really force these things :P