Dash - 8 is one of the safest turboprops ever made - it has fantastic short field performance, I witnessed a demo at Yankee stadium where a D-8 landed on the diamond,periouted & took off again outof the stadium. THe ATR was initially plagued with aileron / icing problems hence the addition of vortex generators to "patch" the aileron effectiveness when iced up.. That being said - the newer ATR's are much improved with composite materials & noise cancellation technologies. Most thought the turboprop would have been a dead issue by now because 1) public perceptions of safety of jets over turboprops & 2) the comparable cost of jets IE 737s, A320 & MD-80s can be had for a song after the collapsing asset values following 9-11. However, with the new Embraer ERJ-170 - a mini-777 for 24 million - I wonder how long turboprops can hang in there ..... smashing bugs ..??
There are still a lot of fields not long enough for jets, are certified but with hard to achieve conditions (LCY), or not allowed RJs for political reasons (YTZ).
Dash8-400's runway length is on the longer side compared to earlier Dashes but since it carries 70 pax not surprising. Both it and ATR42 had various issues on entry to service so I doubt either manufacturer can get much mileage on that score.
Where Q400 scores is speed, at 360kt it's 75kt faster than the Q200/300 (q400.com) because of the PW150A engines. Bombardier claim a negligable difference in range over 60 minutes between Q400 and RJ85/735 and a 25,000 ft ceiling.
ATR42-500 manages 300kt cruise at 17,000ft (from ATR's website) with PW127s.
I suppose the regional jet "boom" is coming to end and turboprops will be more common again. It is a clear fact that even newest small regional jets simply can't achieve as low operating costs as turboprops on shorter sectors. In fact, turboprop market has shown already signs of better future. Many regional jet operators, especially in the US can blame only themself of the current poor economical situation, as they got rid off very economical turboprops and acquired new ERJ145/CRJ200s few years ago just to notice that those good old turboprops were much more economical.
I have experiences as a ground crew of ATRs and Dash 8Q400s... In my opinion ATR and especially the new -500 series is a little bit better product than Q400. The ATR is a real workhorse, extremely reliable even in harsh winter conditions (-200, at least) and very economical. The biggest advantage of especially ATR72 is that it has two cargo compartments. If the flight seems to be tail heavy you can easily put some cargo/baggages to front cargo compartment to achieve better C/G and stay inside the envelope.
In case of Q400 the biggest issue is with payload and C/G limits. It is quite long aircraft and the only cargo compartment is in the back. This means that there is huge moment arm and you are easily out of the acceptable C/G envelope. If the plane is full it is hard or almost impossible to get all the luggages in due the C/G restrictions. You can't even think about to put some mail or cargo in there!
The other disadvantage of Q400 is the APU... it is perhaps the most unreliable APU what I have seen. Therefore many airlines use rather ground power as power shortages from APU are too common. The Q400 had a lot of technical problems earlier and airlines blamed that Bombardier was too slow to correct those quirks and offered too little help for the airlines... Same thing was with CRJ700. However, Bombardier has now achieved to fix most of the problems and reliability is far better, but I'm not too impressed even today of Q400 reliability especially in winter conditions... The advantages of Dash are slightly better range and cruise speed.
As a pax point of view, I prefer ATR72-500 over DHC8 Q400 anytime altough both are good aircrafts. Slightly less vibration and noise in ATR cabin.
I'm also under impression that the operating costs of ATR72-500 are lower and it is slightly more economical than Q400, but I could be wrong...?
the only cargo compartment is in the back. - Dash 400.
Not so. There is a cargo compartment up the front, opposite the Port side airstair door, which comes as an option. Many Airlines have taken that option due to the C of G probs you mentioned, with out it.
Well I fly the Q400 and am regulary flying with Captains that used to fly the ATR. Virtually all of them regard the ATR as the better machine (much to my disgust), usually with reference to the flightdeck, which is apparently more 'pilot friendly' on the ATR with Airbus style switchlights and a radar that works properly! However they all concede to the superior performance of the Q400!