Yeah, slim is really stylish right about now. I'm feeling things might start tilting the other way, but we're definitely not there yet and you're safe going with slim.
Single vents also make it easier to dance. Unless you have a really flat ass, you'll need a vent so the jacket doesn't bunch up. People can make up whatever rules they want, but that's a fact. You don't want a bunched-up jacket when you're dressed to the nines.
I really dislike single vents on anything except a hacking jacket. They got ruined for me
by an area manager at Gieves who said he didn't like them because they reminded him of Americans with plastic shoes.