Both great packs - I have the Variant 52, a mate has the Mutant 38. I went for the Variant as I reckon it's more flexible with the back pocket if you want to strip the lid to drop weight. The V52 is a bit roomy for use as a summer pack - its a pity they didn't stick volume reducers on it like the ones on the base of the Talon 44. If you were comparing the Variant 37 with the Mutant, there's really not much to choose between them apart from that additional pocket on the main body of the Variant. I find it pretty comfy, even loaded up with the back sheet removed and a 3/4 mat folded up and shoved in the sleeve. I've only tried the Mutant briefly around the car park, but there wasn't much to choose between them in terms of comfort with a moderate load of personal kit and climbing gear.