Actually the Mouse is the most "upright" of the bunch.
Can't say if the MB2 or the Deep 5 has more of an "upright" sound--both can capture vibe but both do so much more than that. The differences are more in the realm of bottom vs. clarity.
What do you mean "by so much more than that"? I'm definitely looking for a very upright sounding bass, but am afraid the Mouse 30 will look and feel way too small on me.