Mont St-Anne is the best for pure Dh but they really lack of freeride stunt and trails aren't really maintained. But you have a real great mountain to ride(fast section, steap, technical). Bromont has more freeride stunt and is better maintained but the mountain is less interesting. Some prefer one, some prefer the other. Rdie both and decide
st anne is amazing. the trails are super rocky so they are really gnarly and they have a decent 4x course which is fun. the world cup course is intense to ride. plus there are no lift lines ever so its good. depends if you're close or not tho i guess...
MSA (Mont Ste.Anne) is nice. The trails are fairly long, but there are only 5 trails to choose from. I love the blue jumps/ramps on La Tordue.
Bromont has more trails, but they are shorter. I ride Bromont every Saturday. My favorite run is #7, cross over to #20 after the stepdown/stepup, hit the Bike Park, then cut back into #7 for the drop bridge! But all the runs are great.
Camp Fortune is small, but has some nice runs. Bring cash, they don't take Interac!!!!
Mont Blanc is also small, with some great trails to choose from (not many, but they're building more runs every year).
i know it's not in québec, but if you're gonna go all the way to camp fortune, might as well check out calabogie.
They've got plenty of trails for all levels and sort of a bikepark.
and on top of that the runs are all really really well maintained ( fill ruts and berms every week), and since it's only been open for a couple seasons, the runs are pretty much rock free.