I as well got a Science MS5 44" it has double stringers and is stiff as hell. Great for the bigger surf.
42" is considered standard so if you're just starting go with that, and a crescent tail, single stringer.
Many top companies are now selling great boards for ~$200 which is a terrific price.
Many of the Australian brands are now leading the industry and have some wild new options.
I'll just put out some names/brands and you can search the names easily.
Turbo Surf Designs
Nomad Bodyboards
Mike Stewart Science
NMD Stox and VS
Toys Bodyboards
No. 6
BZ
Custom X
Also, remember that just about the biggest aspect of BBing is swim fins. You'll need these too if you're just getting into the sport.
Viper Fins
Custom X
BZ
Ally Swimfins
Hydro Swimfins
Stealth
Limited Edition
I'm sure you'll get stoked when you see all the stuff these guys have on their sites and they are both ( Jay and Bob, respectfully) very willing to help.
I've had a couple of boards in the last few years, currently I'm riding a Mike Stewart MS7 42.5 cresent tail and it is the absolute best board I've ridden. The rails are sharp as knives, the deck is like leather, and I've been able to hone my drop knee in a short time cuz the board dosent bend. I'm 5'9 180lbs and I wanted a sturdy board. I used to ride a BZ and a Wave Rebel and both had stringers and both ended up looking like bannanas. The decks were soft like foam and they just weren't thick enough for me. I like a thick board but not too thick. My friend has a No.6 board and it floats well but its way too thick and heavy and the rails are not as sharp. I prefer a cresent tail cuz it huggs my hips and it's easy to bottom turn, and slide into the drop knee position. My BZ was battail and I would constantly smash my johnson in heavy shorebreak and when learning to drop knee. Stay way from the wave skate aka lasanga tray, it has a terrible shape, heavy, bad rails, and the deck just sucks. I've taken the MS7 on a few trips and it has taken the punishment of traveling and of me beating on it, and it's as straight and true as they day I bought it. With not even a pressure dent on the deck!! I'm interested in Respect board and the new Congo line of boards, but I might just stick with Science till someone proves otherwise.