OK then.
Dornier 328
SAAB 2000
Q400
... all of which are fast, efficient and cost-effective. Decent flight deck too, with VNAV, EGPWS, and so on.
No real reason to restrict the choice to turboprops - airlines around the world are ditching them in favour of jets - so:
Embraer 145
CRJ
Dornier 328Jet
... and so on.
The DHC-8Q300, ATR 42, and Saab 340 B's are all old technology, and not as efficient as the ones mentioned above.
I haven't flown a turboprop for years, but my pick of the bunch would be the Q400 from an efficiency standpoint, and the Do328 from a fun viewpoint.