What kind of sound are you looking for? The Deering is brash and loud. Reminiscent of a bluegrass banjo. I haven't had the chance to play one for more than a few minutes, so I can't say how easy it is (or isn't) to modulate the volume. My first impression was that I would have a hard time singing over it. YMMV
The Duke 10 is easier to tame, more like a dixieland tenor banjo. Bright and snappy. Makes me want to wear a candy-striped blazer and a straw boater. I'm seriously tempted to get one of these; I wouldn't play it everyday but in the right ensembles and for the right music it's delightful.
The soprano/concert Firefly is quieter, more like an old-time minstrel gut-strung banjo. It's the one I own because I want to be able to sing and play with other ukes without drowning them out. When somebody comes up to me (of their own free will) and says they loved hearing me play, chances are I'm playing the Firefly. People just love it.
I haven't played a Firefly tenor but I sure would like to give it a try!
The Gold Tone BU series are plunky, playable and loud. They sound like... well, like a banjo uke. Vaudeville all the way. Those clear plastic ones look like a lot of fun.
I would say all of these are high-quality instruments (well, the plastic Gold Tones are probably a step down but nonetheless I feel that I may need a purple one). The trick is finding the right one for you.