Definitely the Ray Samuels F-117 Nighthawk battery powered unit. It's tiny but it sounds amazingly good. The battery will run for around 48 hours of playtime before recharging is needed (when new). I love the sound of this unit and for the money I know of no other that can touch it.
I just had my battery replaced after about 4 years of use and it sounds like new again!
Plus all the controls for gain and loading are on rotary knobs right on the front panel. So setting it up and dialing it in couldn't be easier. I uesd to own the Musical Surroundings Nova Phonomena but to my ears the Nighthawk sounds better and the lithium ion battery lasts way longer.