It's about 15 years since LH operated into GLA and even then it was once daily at most, so not great for connecting. The airline industry has changed massively since then so I don't think how that service fared really gives any indication as to how any new route to a LH hub would work out.
In terms of which hub to go for, I would've thought FRA is the one given the new capacity that will be available by the end of the year. MUC, whilst a very nice airport, is slightly out of the way and DUS does not have the connectivity - I believe as well that DUS is very restricted slot wise and maybe has some kind of tight curfew as well?