I have both, and there are so many grades. The AYA is clubbier than the Merkel as a rule. There are always exceptions.
My experience is limited to having owned 3 Merkels and two AYAs, so it is limited.
Which two AYA models have you owned?
Unless one is talking about lower end guns like AYA Matadors, etc which were spec'd for the American market and are a bit heavy and ungainly- the normal English styled AYA models of ANY grade- no4 boxlocks through no. 1 Sidelocks etc handle very well.
AYA traditional builds there guns scale to each gauge. They are as light or lighter for each guage than any Merkel.
The Merkels are great guns, but in terms of mass and balance, I do not see them as being superior at all to an AYA.