I don't think think it's quite so simple as those three options - both sequels have improvements and regressions (DA with net regression and ME with net improvement, I feel), and for the problems, Bioware and EA are likely respobsible for different parts.
Mass Effect 2's gameplay and structure was an improvement over 1 - the missions were more diverse and well-designed, the dialogue was bigger and better by a small margin, the long travel times with nothing happening dropped off, and the combat became more streamlined, and in a good way (they lost originality points, but ultimately it works better than some of the glitchiness of 1 - and frankly, with 1, your guns and abilities were either inferior or overpowered with no inbetween). The Over-arching storyline suffers by being lower stakes than 1 and easily forgetable, but that forgetableness means that during the vast majority of the game, the quality of the small-scale storytelling is front and centre. As far as the EA/Bioware responsibility, I suspect largely Bioware.
As long as 3 stays away from making linear missions and linear mission-to-mission progression, keeps the free-roam areas big, diverse, and interesting, and has a story that doesn't suck, I don't see many ways it can go wrong. And if that does happen, it's probably EA's fault.
Dragon Age 2 was bad for 3 reasons. 1 was the rushed development schedule, which lies on EA's head. 2 was that the story fell apart at the 3rd act, which is probably a combination of Bioware's fault and reason 1, in that order. Reason 3 is that they tried a significant change in style, changing up the dialogue, art style, combat, environment, and story structure. The combat was a slight improvement overall, the dialogue and art styles come out very slightly better, and the environment and story structure came out noticeably worse worse - and when you change things up like that, you have to better than just better overall, because it takes people familiar with the previous game, the largest market of any sequel, out of their comfort zone, and Dragon Age 2 got worse overall - and again, I think that's largely Bioware's responsibility.
They can totally turn it around for 3 though, but it's going to require ANOTHER overhaul, so it's a risk.