The Radium49 and M-Audio Uno aren't midi interfaces, per se, they're controllers, with midi interfaces on them.
Picking a midi interface depends on how many midi controllers you're going to use; for instance, if you have 3 midi racks (Motif rack, Triton rack, Roland rack), you'll need an interface with multiple ports to connect them all to your controller. I think the Mbox only has 1 midi-in and 1 midi-out, which is what most sequencers have.
Here's a list of midi interfaces from ZZounds:
http://www.zzounds.com/cat--MIDI-Interfaces--2429Some are 4x4 others are 8x8 or 1x1.