Hey bellingham,
OK, well here's some comments from someone (me) that's never used a pot puller, so take them with a grain of salt...
I belong to the North Olympic PSA, there are a lot of old guys in the club (think Sequim) that do a lot of crabbing/shrimping. They are divided into two groups: the ones that have an electric puller, and the ones that wish they did.
There are many guys in the club that have gone from gas to electric and never gone back. Complaints I've heard about the gas ones: loud, smelly, cantankerous (even the Honda's) high maintenance, cumbersome, and dangerous... they don't stop on a dime, and on most of them, they have big, hot mufflers that you have to reach across to hit the kill switch, it's usually on the wrong (outboard) side. The complaints I've heard about the electric ones: they are slow, and sometimes weak (older models)
Lots of guys complain that either kind, if it just has a small pulley up top on the end of the boom, and the rope comes down to the motor, lower on the boom, if it's that style setup, they complain that it makes a mess of the boat, the rope slips a lot, the rope is all wet, etc.
The more commercial-style pullers, with the large driven davit up top, they grip and squeeze out the rope and from what I've heard, tend to work much better.
I've also heard that the reason that the electric ones are weaker is not because the motors can't be built as powerful, it's because most people don't run heavy enough wire to the electric motor... remember, you're drawing some serious amps there... so if you go eletric, run super heavy wire.
So I've looked at different puller designs for years, and listened to all these guys, and I think if I were to build one myself, I'd use a big driven davit like the commercial crab pullers, and either put the electric motor up there on the davit on the end of the boom.
Or get a electric-hydraulic pump, like those used on snowplows and such, and mount the pump near the batteries, and run hoses up to a hydraulic motor mounted on the davit on the end of the boom. Of course if you had an inboord engine, you could probably mount a bracket on that and run a hydraulic pump off your inboard engine to power the puller.
Just more food for thought.
-N.