NotSo - you are mistaken about BA's A318s. The reason why they cancelled the order has more to do with the PW4000 engine development problems. Air France, which insisted on having a de-de-rated version of the CFM-56 instead, is still looking forward to take delivery of their first A318s this year, to replace about two dozen 737-500s.
While the A318 is indeed too heavy for a single-type fleet when compared to the 737-600 or better still, the 717-200 (né MD-95), it makes sense for an operator that already uses other fly-by-wire Airbuses, because of the single type-rating with the A319, A320 and A321 and fleet commonality for maintenance.
Therefore I think Lite would be a better bet than DUO since MYT already operate the A320 and A321 (plus the A330-200). However, some senior ops. people at DUO really fancy the Airbus...
Cheers