You're right; they're not readily comparable.
DA is a single-server solution and H-Sphere a multi-server solution.
But don't forget that H-Sphere is priced on a per-user basis, and that a user is defined as (from their website): "admininstrative, reseller, reseller administrative or user".
Many users can create other users, see
this page. So you should always have an extra us$112.50 on hand so you can buy 24 more users when you run out.
Support is extra, see
this page.
And for those of us in the U.S. who might not be satisfied with support only until 4 pm on the East Coast, 1 pm on the West Coast, 24/7 support costs a minimum of $300 per month.
They recommend a minimum of two servers, though H-Sphere can run on one server.
And they're very picky about the OSes they support:
From their website: "For example, Red Hat 8 and 9, Fedora, Debian, and Mandrake aren't supported."
The only smtp server they support is qmail, and after my experiences with qmail and Plesk, I have to say that's a reason for me to have second thoughts.
All that said, though we do offer support and services for H-Sphere, though that's a topic for another forum.
Jeff