SPB Mobile Shell is WAY better than Sense. Not even close.
You can customize Mobile Shell however you want, easily. Plus it's more stable and uses less memory. You don't have to hack it up either, it is totally customizable out of the box.
Check this video out:
http://www.youtube.com/watch?v=IGrfQ7IKGBs
And that video doesn't even do it justice. Look at this thread to see some awesome themes for Mobile Shell:
http://forum.xda-developers.com/showthread.php?t=566045
And keep in mind, this is all using less memory than Sense.