Dive Propulsion Vehicles (DPVs)
I absolutely love my Dive Extras Piranha (discontinued)! Before that I loved my first scooter, the Dive X CUDA 400 (also discontinued).
If I didn't already own two scooters, and wasn't going to go below 300' anytime soon... I'd opt for the equally amazing, and far less expensive option: the Dive X Blacktip Tech.
You'll notice all these scooters are from Dive Extras. I'll admit, I'm biased. They're a pacific northwest local company (up in Everett), Ben is a diver who's super passionate about building the best products, and they have amazing service. So while other great scooter brands are also amazing, I'll be sticking with Dive X.
The Tahoma Benchmark Tests are your best bet for raw data. Each year different scooters were tested, so if you’re trying to read up on all of them, you’ll have to read all three reports.
2011 [read the paper now] [demystifying the results, from Logic Dive Gear]
My recommendation would be to find a friend with the scooter you’re interested in diving, and dive it.
While I love my CUDA, everyone that spends $2500+ dollars on a tool loves the one they selected. So asking people which one is best isn’t going to yield you too much of a delta from simply looking at the scooter they purchased already.
Scooter Manufacturer Links
Dive-X Scooters Blacktip, Piranha, Cuda
Gavin Scooters [the Classic old school Cadillac of scooters]