I've applied to Qatar, and I would come if offered the 777 or A330. But I don't want to leave the United States to fly an A320 at QR, when I could potentially line up an interview at JetBlue and fly the same equipment here. But in the US, no one in their 20s is on the 777s or A330s. Getting on that equipment can also open up more options for later, beyond QR if one chooses.
Another bad thing I've heard about QR is the "bait n switch" trick. They offer you a 777 class, for example, and you leave your airline to come to Doha. (The bait) And once you get there and everything is too late to change or go back, they switch you to an A320 class. (The switch)