I've worked in the ground handling / operational environment exposed to both these types.....difficult call!
If you compare the 'classic' Dash 8's then my preference is with the ATR any day. However, throw the new dash 8 variant (Q400) into the equation (although they have had reliability issues!) and the ATR starts to look quite date in terms of speed, range, etc.
I still love the ATR72 though.....despite its imperfections!
(edetid for spulling)