There's not many things the B3 isn't better at, IMO, other than price on the used market. The B3 has much better amp sims and EQ options, it can do three FX at the same time (M5 can only do one....M9 is a better comparison), I preferred the tuner on the B3, (hated the tuner on the M5). The M5 has a much better footprint as it's half the B3's size, though.
To be honest, I didn't get much into the FX. I was looking really just for something that could do an octave up pitch shift (kinda saw everything else a lagniappe). Neither one sounded all that great doing that and I found an individual stomp box that could. Now I'm looking at them and I could get a much cheaper tuner......and not really miss anything else on it (I have everything else covered on my board). I never really dove that much into any of the modulations or delays.
The B3 is built for bass, though. Line 6 tends to make things with only guitars in mind.
To be honest, I didn't get much into the FX. I was looking really just for something that could do an octave up pitch shift (kinda saw everything else a lagniappe). Neither one sounded all that great doing that and I found an individual stomp box that could. Now I'm looking at them and I could get a much cheaper tuner......and not really miss anything else on it (I have everything else covered on my board). I never really dove that much into any of the modulations or delays.
The B3 is built for bass, though. Line 6 tends to make things with only guitars in mind.
