I like the one that holds waste water and let's me haul just the tank to the dump.
I prefer the two wheel version because where I camp is not paved and two wheels are easier to deal with than four over rough terrain.
Barker= good
Tote-n-stor = good
Thetford= good
Pick the best deal you can make and enjoy the convience of not having to break camp to do the dump.
Don't overthink it...it's just a poop tank.
Thanks!
Jeremiah