Breck's jumps are way better and everything flows better in my opinion. Keystone has a much bigger selection of rails/tubes, many of them being set up pretty unique (some are kinda gnarly but can be very fun).
As far as efficiency and ease of skiing, Keystone is better because of the park lift, whereas Breck's lift services other trails besides the park and it's at the busiest base of the mountain. However if you're skiing during the week Breck is prime because the amount of people there is minimal compared to weekends. I'd suggest to check out both while you're out here...Keystone's park is also open until 6pm for night skiing which is always less crowded.