I wonder how the EMB-170,175,190,195 models are faring? Last I heard they're supposed to be pretty good.

Regarding fuel efficiency, I think whenever planes will get the new P&W geared turbofans they'll win the cake. Although, the defining factor among that group is which plane has the slickest airframe.
Pratt & Whitney: Commercial Engines - PurePower PW1000G

For airlines better fuel efficiency means nothing though unless other operating costs and investment costs stay the same or reduce as well.