Having flown on both, I'd give my thumbs up for QR over SQ. Really !

But what matters to you will be of course on where you'd want to dump your points into which FFP programme.

QR's service and food trumps over SQ. And I would also say their IFE has a better range of films that SQ's.

QR's fares would also tend to be much less than SQ's. The Premium terminal in DOH is a cinch to transfer and is very good to relax.

You may read reviews of QR's services here : http://www.airlinequality.com/Forum/qatar.htm