I am travelling from BHX to LAS via Germany soon, and my choice seems to be between UA and LH for the transatlantic sector.

I have some UK *A upgrade vouchers, and I am a BD Gold *A member.

Should I book UA or LH for the transatlantic sector?

Will UA only upgrade to Econ+ when using the voucher, or will they upgrade to business class as I am already entitled to Econ+ because of my BD *A Gold?

If I don't manage to get an upgrade to business (none available) I assume I will be better off on UA in econ+ than on LH in regular economy?

What would you guys do?