Personally I like the BT7 because it has 6 settings. I think of them more as "feel" or comfort levels, you can pick which one works best for you. When I am in a bad emotional state I find doing three consecutive sessions on setting #3 will cause an endorphin release which is much better than drugs. I am not sure if it will do the same for you. The ear clips also are fairly comfortable to wear. My brother tried the Alpha-stim and did not like the feel/pressure of the ear clips or how the settings felt on the unit. He also prefered the BT7. CES ultra looks OK but I like the idea of having more comfort settings.
If you are able to join this yahoo group it is the only one that has some reviews of the CES units.