Boeing is cheaper about maintenance but not in consumption.
So A320 after sale maintenance is expensive but its more fuel efficient . . .
The A320 also happens to be comparatively expensive to buy.
As far as technology goes i understand that the fly-by-wireyness is all the rage these days but as a pilot i have to say it makes little difference.
Take off , set the Autopilot , both have great Fmcs and will maintain ANP of less than 1NM , get to the destination and do a manual landing ( or an autoland if you're lazy
).
Also I think there are some sale/leaseback advantages to the a320s ,do the buses get a better deal while leasing back ? I know some LCCs make a chunk of their profits through sale / leasebacks .