I have played ME:2 and some ME:3 and I am currently playing DA:O and I voted Mass Effect because of what I have played, I prefer Mass Effect. It made me much more excited to play and kept my attention a lot more. But my opinion may change once I play more of both series

I do think its funny though because I prefer fantasy medieval settings to other settings generally but I prefer Mass Effect to Dragon Age (so far) and Fallout to Skyrim, which also has a more fantasy medieval setting