My preferences:
1. Separated (tentable) vertically staggered columns with angled thumb clusters (like my DIY board and AcidFire's Nexus)
2. Separated (tentable) vertically staggered columns with thumb buttons (like ErgoDox)
3. Combined (flat) vertically staggered columns with thumb buttons (like the picture above)
4. Combined vertically staggered columns / Symmetrical stagger (like this:
http://i54.tinypic.com/adyfbs.jpg)
5. Matrix
6. Horizontal stagger (normal QWERTY)
So for me, matrix layout is only one step better than "normal" layout. I do have a problem with the ErgoDox and possibly nexus, though: The pinkie columns need more offset.
That is all..