Which is better...

Go into Camping World. They are all set up, try each one. You may have to make 3 trips waiting for build up in your system.

I just bought the "Camco" deluxe 5 gallon model with the pump flush instead of the bellows system. Got it from Amazon and compared with everything looks like it will suit us. Haven't used it yet but will this coming weekend for a family cookout at our new camping location. We just bought a couple acres on the river near us and wife and I can spend a few days there with no problem with tank capacity. However a family party can be 10 or 15 extra and don't want to have to take MH to dump before we are ready to head home. Jim.

By "portable toilet" I presume you mean a porta potti? :h If so, the Reliance brand appears to be a basic hassock style toilet that captures waste in a bag :E so unless you're looking for a really cheap solution pass and get a porta potti that flushes. We had a Dometic porta potti but didn't care for the method of pressurizing the tank with air which allowed for "power flushing". The best we owned was a Thetford 585 electric flush model with a 5 gal waste tank but it's no longer produced, in fact it appears Thetford now offers mostly just bellows flush with most models. If the cost isn't prohibitive and you have the room for it I'd say your best bet would be an electric flush Thetford Curve.

If I was buying one it would be the Thetford Curve. Seems to be the only one that's the same size as a normal toilet. Electric flush and it has a swing out tube for emptying that seems to me would be necessary.

Camco, seems popular on Amazon.

I'm sure Amazon would be a good resource.