Fleet commonality vs introducing "more efficient" type
With fuel costs reaching new heights and the market becoming more and more volatile, I was wondering what would be the best choice for an airline (let's say LCC) in terms of fleet choice.
I take for example the A318 versus Emraber's 190-195. In an airline that needs the A320-321 for dense markets but has also niche markets that require smaller aircraft, can Emrbaer's fuel efficiency -along with 19min turnarounds- outweigh Airbus' advantage in terms of fleet commonality and therefore savings on training, maintnenace...?