I'll throw out another brand that I have. Tot-N-Stor
This is a PDF down load of the Tot-N-Stor
And here is a place I have bought many hitch parts from that has great service, free shipping on larger orders and great product writeup's
See here for write up's
Amazon sells them as many other places. Regardless of brand, shop around for the best deal and do not forget the shipping costs. Some are free, others are not.
These are good quality. They have good rear wheels from the factory. They are a more of a rubberized plastic wheel with a tread pattern. They do not, rattle going down the camp road to the dump station. Other brands have more of a hollow hard plastic wheel and it really "advertises" that your heading to the dump with your blue tote.... If you get one of those, load rollers, many folks have done the air tire rubber wheel upgrade and they roll quite and push easier then. See Jim's link, I saw his and he did a good job on that.
I have had an 11 gallon Tot-N-Stor since 2003. We had it starting with a pop up for sink drain water. When the TT came, I had it and still use it. It is way too good to get rid of and in my case, I do daily camp choirs and every day or every other day do a gray tank run when we are on extended camping trips just to stay ahead of being full. I have not yet come to grips with the need to upgrade and spend more to get the larger capacity. If I was starting out with no tank, then I would go larger.
Barker, Tethford, Tote-N-Stor are all good brands. Each have similar features some are different. You really cannot go wrong with any of them.
As to the size, this is where there is more debate on, what is the right size for "your" needs? 2 wheels, 4 wheels, the options while not endless are many.
In my case my 11 gallon one is still working well. It is "just" large enough to be effective for "my" needs and I can either tow it to the dump or lift it up in the truck bed and haul it. But it is about the limit of the lift it series. It is close to 100# filled and that is all I would want to handle.
If I was to ever buy another one, and some day I will as hoofing 100# up into the truck bed is not in the cards, I would look more in the range of 25 to 30 gallons. I had a buddy let me play with his Barker with just water to see how managing some 200# plus of a tank, was going to be!!! It was a 2 wheel version and that style you had to lift it to pivot it to dump. Your still lifting ~ 100# of one end of the tote. The longer the handle the less the lift but still, it was an "amount".
If and when I get one, Tot-N-Stor is the brand and I would get one that had a dump valve that I do not have to lift the tote. Just pull the valve.
The other part about which size? Where to store it? The bigger it is the more room you need. On our long extended trips which is the only time we take one, mine goes in the truck bed. Again being small it fits and on these trips there is usually more "stuff" in the bed anyway making getting a larger one even more of a space issue. If and when a larger one comes, I will have to figure out how to store it. Maybe a holder to go up under the camper. Again in my case I have a larger camper with a deeper 10" frame and can store stuff up in that space. A small lo rider camper, that may not work.
So, think through all these "how to's" pick the brand/size you think fits your needs and get one.