Impossible question. It's totally up to your ears man. Mesa and Soldano are cut from 2 separate cloths. Mesa is a great amp, great tone, and have been aroundo many a band and stage and studio. Soldano is a special breed - they're unique and rightly so. But you can't compare them as similar "AB/Y" amps. They're very different.
Personally because I like and dig "unique", I'd go Soldano. But that being said, I've owned an SLO and a HR100+ and I don't have them any more. I've had a few Mesas come through my session space as well, and at best they were 'meh' to my ears. But the 'meh' is good - it's just too common for me.