Well, with your desired route being SFO-FRA, that pretty much eliminates non-Star from the conversation.
The question might then become whether LH M&M is a better program for you than UA MP. (I know zip about LH as a primary program.)
I think of the "pros" to UA as being reliable access to E+ on UA metal, low taxes/fees on international awards, fair SWU requirements if you ever hit 1K (or otherwise acquire a SWU from someone), and relatively good award availability on UA metal. (By "relative" I mean about as good as AA and better than CO, DL, or US.)
I think of the "cons" as a primitive website and Starnet blocking. The latter would affect you on SFO-FRA, as in my experience LH is one that gets blocked quite a bit to/from the U.S. (By "Starnet blocked" I mean that LH is offering up award seats to Star Alliance partners but UA will not book them for you using UA miles. The phone agent will say things like "that flight doesn't even exist in my system" - very annoying.)
Originally Posted by wco81
As for getting the AA offer, if I go UA, I can't imagine ever flying AA or OW, maybe Qantas if it's AA code-shared. So I'd have to maintain those miles and after spending to get those miles, I can't imagine using those AA cards over my Schwab Signature Visa.
I hear ya, but I still think if AA said "Here, please take 75,000 free (or nearly free) miles", I'd accept them.
Worst case: one of your Europe trips goes one-way in biz on AA and one-way in biz on UA. It's a nice backup to have if you're getting stymied on award seats in one direction. The AA-UA combo is powerful because both will let you do one-way awards.
Besides, there are always easy ways to add AA miles. They have a bazillion partners and there are always hotel and other promotions.