The only benefit you'll have, as A3 currently doesn't pay an Elite bonus, is when *G lounges are better than business lounges. This is pretty much restricted to LH, so if you choose Business with them you'd be slightly better off. It's probably a long shot given there's very few occasions when you'd choose LH in Business ahead of almost any other *A carriers, so I would tend to agree that you should concentrate on miles accumulation v burn rates.

You might actually find that A3 is more generous than LH in that regard - most Business classes are 2x, whereas M&M is moving towards 1x on discounted fares. It really does depend on exactly who your travel is mostly with, and how often you sit in F compared to discounted C.