You can earn UA miles on EK MP. QR miles are best parked in LH M&M.
EKs C product is weak if you get one of the older 332 or 777 service. EK is one of the few airlines where an airbus does have a middle seat in business (remember the campaign about 8-10 yrs ago?). EK's DXB hub is hopelessly overcrowded, but their STPC programme is great and free if you are travelling C!
QR should have a better C product, terminal etc.
LH runs the service using their brand new 333s. Note that on multi leg trips with the same flight number, you only get the FRA-DOH miles.