I’ve got a Soul and a Slackline. They’re both awesome in different ways.
The Soul has a more XC feel to it. It’s lighter, feels more nimble and more comfortable on normal rides. I’d say it’s also slightly better finished and just feels ‘nice’. It’s great.
The Slackline is heavier and a lot stiffer. It holds lines better on fast corners, jumps better and feels better downhill. It’s also great.
I prefer the Soul for XC rides, but the Slackline for downhilly stuff. That said, I’ve ridden DH, raced enduro and done 24-solos on both and it’s been fine. You’ll not go wrong with either.