The bag you need really depends on if you are commuting or not. If your commute will be on crjs, 145s, or dash8s, you will need a tougher bag as going in and out of the baggage compartment destroys a bag. I've gotten away with a Luggageworks ballistic nylon flight case from the StopOverStore. I commuted for a year and half but have been home based for 2. Its held up pretty well and isn't too expensive.

The 170 will hold any size flight case but if you get one with wheels, it seems to interfere with the armrest if you put you jepps on top of it and you sit low.