Dragon Age do some things better than Elder Scrolls,but Elder Scrolls do more things than any other game.
With Dragon Age you can expect the usual Bioware traits,like a good story and cinematic presentation of very well done dialogues with npcs like in Mass Effect.
With Oblivion you can expect the usual Bethesda traits,like playing one of the largest games out there,a game that you will be playing for months always having something new to do.
If you want a medium sized cinematic experience go for Dragon Age,but if you want a really huge game that will keep you busy multiple times the time you would spend for any other game,go for Oblivion.
Personaly I would suggest you to play both starting with DA:O and then playing Oblivion.
It's important to play an Elder Scrolls game last,because it will take you most of the time,and after you finish with it you will have a strange feeling when playing other games, that they are very short.
I was an FPS fanatic before playing Oblivion,and I decided to play it without much thought,but after playing it,it made me feel that FPS games where ridiculously short and spolied all the fun I would get from an FPS's single player mode,'cause after Oblivion FPSs and other short games felt like large demos instead of full games.
Proceed at your own risk.