Ana, I've 'done' both boats (Juliet-Bahamas-summer '05) and SPREE here in the TX Flower Gardens MANY times and although I enjoyed all my trips on each boat, overall I prefer SPREE. JULIET only carries 12 divers max, but JULIET is an old (1970) converted boat (as in never designed for scuba originally) and is very cramped, I'd say there is more useful space per passenger on SPREE......navigating/climbing around JULIET below deck is like being crew on a U-boat....very tight! Also the SPREE dive deck is under permanent shade, meaning no baking in the sun or being in the rain/elements like JULIET's completely unprotected deck (unless JULIET erects it's 'tarp') SPREE is also a lot more camera friendly. (dedicated/protected camera area)JULIET is also much slower, although sailboats do look kinda romantic.
I'm not anti-JULIET (JULIET was a great trip and it was my very first liveaboard trip, which got me hooked on liveaboards) but I think SPREE is a better designed scuba dive boat. Also Capt. Frank/Melanie of SPREE doesn't babysit divers, once you demonstrate to them you do have a 'clue' about diving, they will cut you a lot of slack, their only real constraints on divers were don't bust their max depth limits, and don't run out of air......you don't even have to get back onboard with 500 psi or anything like that, if you can take a breath off your reg after you exit the water, then your 'golden'.
Karl