The M500 will likely sound much better (you can’t really compare wired vs wireless though). I own the Backbeat Pro 2 and while they’re very confortable and the battery life is amazing, I feel like the sound is just good, not amazing. IMO, the $80 Jabra Move headphones that I use at the gym sound slightly better.
I am trying to convince myself that I don’t need the M500’s. RFD is going to ruin me haha!