Well, I don't think you can really go wrong with any of these. Personally I like the general idea and attitude of Schiit as a company here in the US, so I didn't do that much looking around when I got my Asgard.
It's a bit hard to express, but in my mind the Magni is a good stepping stone, a good way to find out if you like solid state (and Schiit in general). However, I don't really see it as a destination, which (sort of surprisingly) I actually think the Asgard is more of, even at its price. Sure, there are lots of better and more expensive amps out there, but even having gotten to listen to a lot of them there hasn't been anything that I've heard that I felt like I really wanted/needed compared to how well the Asgard already performs (with my cans and ears, standard disclaimer and all that).
Still, to reiterate, they're all good amps. And do keep in mind that Asgard was my first amp; I've been to a number of meets now and heard some stellar equipment, but part of my love for the Asgard is certainly just because it's what I got first and is what I'm used to.
Excellent....thanks! Strong endorsement.