Honestly, I've been pretty lucky with conflicts in the past. The only one that's been a huge bummer in year's past was in 2011 with A Day to Remember and Bad Rabbits (went with the latter). Other than that, I've been content.
To be honest, Bad Rabbits was the way to go. I've been following them for over 3 and a half years, and they work their fucking asses off, plus their live sets are always so much fun!
The only major one I had was Tonight Alive playing at the same time as I Fight Dragons (and then IFD's set rolled over into Mayday Parade's set), but I went with Tonight Alive then went to Mayday. (It sounds weird, but TA was at 11:45, IFD was 12:00, and Mayday was 12:15.) I'm glad I chose what I did though, TA and MP were the two best sets of the day for me.