Re: Best inflatable toy/ski tube?
It's all a matter of preferences, I guess. I like the round tubes in the 54"-80" range. It's a good all around tube that anybody can ride and isn't scary looking for the meeker crowd. Most of them are vinyl tubes and price usually is dictated by the thickness of the vinyl(expressed in "mils") with thicker obviously better. Most have a nylon type outer covering which is where the tow rope is anchored and any grab handles are attached. The covering also closes off the hole in the center of the tube from the bottom so you can sit with your derriere in the center securely without it hitting water. The better tubes have an inflateable floor section that gives a little extra padding. Mines doesn't, but I usually palce a throwable type seat cushion in there; it works well and doesn't fly out even on hard spills.
We also use a jetski-type towable, and it's good for the little ones and anybody who wants a really mild ride, but you can't swing it out of the wake very easily, so it can be a boring ride for more daring riders. It also doesn't jump very well. The only thing it does well is bounce fore and aft a lot. Which has it's advantages at times

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We also have one of the two person sitting side by side jet fighter type towables, and my opinion is they're dangerous. We already had incidences of heads being knocked together and missing teeth. So we don't use that one very much anymore and I don't recommend them for any but the most gentle towing, like in no-wake zones where people just want to ride out back and get a little wet going from the launch area to the real ski area or whatever. Or maybe a really young one wants to ride next to mom or dad and you're going to go real slow anyway.
As far as brands, they're all pretty good. My round tube is an O-Brien I got from K-mart about 9 years ago, we use it hard and it's still going strong. The graphics faded a little and the foam on the grab handles is gone, but the tube still holds air and the cover hasn't torn anywhere.
Anyway, that's my 2 cents, for what it's worth. I don't have any experience with any of the newer style tubes like the Sumo or Twister or any of the chariot style tubes so I can't help you there.
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Stan