I have both a Thetford type porta-potti, as MadJack mentioned and one of these:
We use the Thetford type porta-potti that flushes in our bigger trailer where it can stay in it's closet until I get it home. What I like about this one is it "flushes" everything away. Say my folks stop by on our property without toilet facilties, they could use this one too.
The bag style... well... you'd have to hand them their own bag
The "Pett toilet" is what we use strictly with the teardrop. Let's face it, a "bag" is a "bag" and maybe none of the "Let's make this smell nice" formulas are going to perhaps live up to our expectations.
What I like about the Pett toilet bags is they have some great "stuff" in them that seems to work pretty well and they fold up into a really strong outer bag for easy disposal.
The main downfall is they are VERY expensive.
A plus - VERY portable. I don't want to lug the Thetford style toilet in and out of the tow vehicle or teardrop with all it's chemicals,etc.