Was in QR a long while ago(Skipper Widebody). STAY away. I do not believe that this guys are ever able to change. Alone that command comes earlier and the "package" is a bit better(except housing) speakes a clear language. They need pilots because they are loosing them. Always have, even 20 years ago. Back then most just "jumped ship" means they never came back from leave, disappeared during days off or during a turnaround with layover out of Doha. And this guys had very valid reasons to do so.
Now, the advantages of EK have been already mentioned and I fully agree here. Doha is a SH, Dubai, well, after one week I always was happy to leave as well. Both places have that "middle eastern charme" that you either like or...NOT. But clearly Dubai is the better choice. It is actually like choosing the painless shot in the head(Dubai) or getting that knife very slooooowly and gently pushed in your brain(Doha).
Time to upgrade speaks a very clear language as well. I you do not know what I mean let me explain - companies like Ryanair, Qatar offer VERY fast command upgrade. What you think why? Because they like you and want to see you with more money and that fantastic 4 stripe with all the nice responsibility for everything and, all considered, not that much money for that responsibility? Or is it because they expand AND loose pilots every month?
Then there are carriers with a longer wait time for command - because they have enough people(well, at least more then the crappier carriers) so they can afford to have experienced skippers(not 3000 hour guys) on the left and having a very close look for the "new generation" growing to experience on the right hand seat.
IMHO deciding to middle east is ALWAYS a long term decission - you cannot just go there for 3 years. You have to be in for at least 10 years or till one of the magic to buckets are full(you know, either the one with the money inside or the one with the s..t).
If it has to be the middle east - go EK. Or Flydubai(even the night flying will kill you eventually, but this will be the case on Longhaul as well - tried it, did not like it).