Q400 - higher, faster, crankier
Q400 is a high speed turboprop in the same class as Saab 2000. Will do 360 knots with their PW150 engines as opposed to the ATRs 277 or so. The Q300 (ATR42 size) has PW120 series engines and so the cruise speed is more or less ATR-ish.
The Q400 variant has been selling slowly - QF have taken some recently, but no sign of Air Canada trading in any Q100/200/300s yet which would be a vote of confidence.
ATR have been doing well sales wise. They claim payload/range improvements over the -200 and a quieter cabin with bigger bins. I also seem to recall something about icing performance in the -200 but can't swear to it. Anyway lots of stuff on the website.
I expect it would take a hell of a deal to make RE move given the commonality with the -200s and the variation within the Q series.
www.q400.com
www.atraircraft.com