Instead of the ATR-42 you should have a look at the Dash 8-300, leasing is about the same, fuel consumption is better and it can transport more passengers.
Instead of the ERJ-140 I would go for the CRJ200, even if the leasing rates are higher, fuel consumption is much better and its bigger.
So I would go for either Dash 8-300 or CRJ200, depending on the routes you plan to fly, if its below 1000km I would definitely take the Dash.