Have ridden both, though not extensively. GF has a Sherpa and have briefly ridden someone else’s Solaris.
I’d have the Sherpa every day. Slightly shorter back end, slacker HA and steeper SA, and it feels livelier to ride (the Cotic feels a bit dead IMO, like other Cotic’s I’ve owned/ridden).
Don’t be tempted to stick too long a travel fork on either and ruin the sharp handling!
FWIW, if the Sherpa’s BB was 10mm lower and they did an 18″ size (I seem to fall inbetween their 17 and 19″ sizes) I’d have bought one myself. The BB’s on my own bikes are loooooow though so wouldn’t suit everyone.