We have fitted over 100 Mains in the last 5 years or so including the Eco combi, the old b rated combi, the old heat only open vent boiler, the new a rated version and their system Eco and they are now our first choice whereas it used to be Worcester and before Main was just our budjet option.
Main have been more reliable, are very popular around here and they're easy to sell being built in UK with 2 year guarantee.
Their after sales is great and the reps the best I have dealt with, try for yourself and see.
Now if somebody wanted a real top end boiler then I would probably consider the upmarket Baxi's due to their stainless heat exchanger but to date the Mains hasn't faulted us yet! Only replaced diaphragms on the old b rated combi's.
We will have fitted 2 Main HE A's and 2 Eco combi's in April alone by the end of the week, I know this sounds like a sales pitch but if Baxi's alternative is as good them then I wouldn't hesitate to install one if I were you.