IMHO, Older Merkel's - great (if they fit you). Newer Merkels - Ok!, but not great (If they fit you or not).
AYA's - Generally better balance. Mechanical quality about the same as Merkels. Wood on Merkels, generally, though not always, finished and fit better.
Given a choice (which I've had), give me a Parker Reproduction or CSMC RBL over either!