No experience with the electric models, but 5 or 6 years ago I bought a Simoniz gas model when CTC had it on sale for like half price, threw in my CTC money and got it for free.
I'd say go gas over electric for portability and power, always better to have it and not need it, over needing it and not having it.
I don't have an overly powerful model, but if I'm not careful it can dig into the deck quite easily.
Likes : portable, powerful, relatively in-expensive (CTC will always put stuff on sale, you just have to wait), on-line addition of soap into the stream is nice, two levels of power, adjustable spray pattern (from wide to narrow)
Dislikes : like any small engine, sometimes its hard to start, the more expensive models have on-board tanks for soap etc, mine just has a hose that you stick in the jug of chemicals, sometimes you have to be careful when you move the washer you don't knock over the jug, but most times the hose is long enough so it's not an issue.
I'll have a look to see which one I've got, but I don't think it's even available anymore, but there will be something like it out there.
Hope that helps.