Given it's an R wave, and Warren consistently underperforms other Democrats in Massachusetts, I think Brown narrowly wins.
Scott Brown (R) 49.96%
Elizabeth Warren (D) 49.87%
Markey got 62% of the vote and won every county in the actual 2014 election.
I don't think she would have lost. Nationally it might have been a Republican wave year, but Massachusetts seemed to be pretty much immune to that. You might say that an incumbent Scott Brown would be stronger, but still, I doubt after having him there for a few years that most Massachussetts residents would still want a Republican in that seat. Warren is certainly a stronger candidate than Coakley, anyway, and 2014 was a slightly less Republican year overall than 2010. (More Senate seats were picked up but that had more to do with the map; their House vote margin was smaller). So if Coakley barely lost in 2010, I imagine in 2014 Warren would win.