You didn't mention what kind of terrain you're looking for. From an expert perspective (looking for steep, ungorromed stuff), I like Whistler better. Blackcomb is good for going back on the glacier, but it has a wicked long run out.
Whistler has the goods all over Harmony and Peak chairs. I would guess there is a lot of snow right now, so some good cornices built up on Harmony. Just keep going further around the ridge to get to smaller cornices. Also some good trees (tight, big trees, so somewhat slow skiing - not Steamboat stuff) just below the cornices off to skier's right. You can also drop off skier's right from Harmony ridge for some good steep stuff.
Peak Chair has great stuff all around. Go to the right when getting off the chair. You can drop in under the lift (Lifties Leap) or anywhere in the bowl. You'll see where you want to go from the lift. Also, if you traverse around to the right (as observed while riding the lift), drop off the back of the ridge, and keep traversing quite a while. I think they recently named some of the tree lines in there. Very steep tree skiing, but if you go really far around, to the steepest stuff, it's two lifts to get back (I think it's Red(?) chair to Peak chair). Once I even managed to end up at Creekside. What a PITA.
At Blackcomb, look for Secret chute on the trail map, just to the right of the chair that you would take to get to Spanky's. It's hidden from view of the lift by ome large rocks, but it's steep goodness. If you go into Spanky's and want some wild stuff, Calvin & Hobbes Chute is fun. It's not on the map. Go through Spanky's entrance, and follow the ropes up the ridge to the left. Just keep going till you get to the end. Strap you skis on and find a way in. When I did it, it was about a mile of bumps, but starts out seriously steep, and not too bumped up, then open us to enldless bumps. On a pow day, it would amazing (until you hit the runout). Also, take the t-bar and hike up to Blowhole. It's sort of like the world's larges and steepest half pipe.
Have fun. I'm jealous.