I don't use reverb live and don't record w/it from the box, so I couldn't help you there (it def doesn't have some of the unique reverb effects that the M13 will give you).
Haven't used the Kemper's wah. I have used the M13/9's Weeper model and it was fine for my uses (provided that I set it to where it wouldn't "open up" all the way).
Of the modulation effects that interest me (namely tremolo and rotary), I prefer them on the Kemper. There is no Univibe on the Kemper, but the M13/9's Univibe is also the worst effect in the entire unit.
The delays on the Kemper are fine, though I'd take the M13's over them for most sounds. Fwiw, it's popular to diss the Line 6 DL4 because (supposedly) it's become obsolete or whatnot (fwiw, a modded one is absolutely necessary). Well, the DL4's Memory Man model (the "modulated delay") is noticeably fatter than (and not as irreparably-bright as) the M13's version of the same effect. For that matter, you can't even come close to that sound with the Kemper. There is a single knob on the Kemper for modulation in the repeats (no separate depth and rate control), and it's just not to my liking. Who knows... maybe that will change sometime. But for now I'd take the DL4 over both of them for delays, but between the M13 and Kemper's delays, the M13 can do what the Kemper does just as well and some that the Kemper can't do (though if you kinda want bread-and-butter delays, you'll be happy with the Kemper).
Obviously the M13 can do plenty of crazy filters and unique stuff (from all categories) that the Kemper doesn't have.
Now, all that said, if FOR ME it were between keeping my M13 or selling it and thereby being able to grab a Kemper (not sure where the rest of the money will come from, so that could affect my decision), I'd bail on the M13 and grab the Kemper. The Kemper is really really really really really really really really cool. I've gigged with it since the day I got it. Loved every minute of it.
Really cool.