Out of all of the Combat Devices,my most favorites were:
Mr.Zurkon-A Combat Device that can not only help you,but entertain you as well.
Groovitron-Again,another Combat Device that helps you and entertains you!
Leech Bomb/Mega Leech Bomb-A very useful Device that can really help you when you are low on health.
Confuzzler Gas-A fun Combat Device that distracts enemies,making them attack each other.
Transmorpher-Yet another Device that entertains you,especially with the Groovitron.
My least favorites were:
Visi-Copter-This device may come in handy at times,but can be kind of confusing to control.
Death Springs-This Device may be useful against groups of small enemies,but is useless against big enemies.