The commercial wizard at our place has worked with both fleet types.
He said that the Q400 can mix and match with regional Jets. Ie for a 2 hour jet sector and something goes tech or loads are low you can switch it out with a Q and still not have to pay comp. ATR its not really an option.
1 hour to 2 hour sectors on the dash you can get an addition 2 sectors out of a crew and 4 out of the aircraft in a day.
He also said the Q kept route integrity which was explained to me that if you planned everything at 220knts indicated on the dash at FL240 or FL250 then if you got hit with headwinds. The dash you had the option of dropping down to FL200 and just taking the hit for fuel and blasting it (Vmo 260 knts indicated cruise at Vmo -10) . Meaning you only really started to struggle keeping things on time when the headwinds went over 50knts on the way home. The ATR was stuffed even with modest 25 headwinds. Not a problem on sub 1 hour sectors for it but when you got to 1:30 -> 2 hours it would cause huge rolling delays. An if the wx stayed the same for 3-4 days then crewing became an big issue.