Baby Bjorn...
I used this for both my kids... and it was perfect for them. My kids are big.
My son for example: is 3.5 and he was using & still does use the Baby Bjorn potty chair high-back, and he is 39 pounds.
- if you notice the baby bjorn is a 'sitting' type of potty chair. And the Potty Patty is "straddling." I think, sitting is what a child will need to do anyway, on a toilet etc. and to me the Potty Patty chair looks more "snug" perhaps... I don't know about the "fit" of a child on it.
I also would recommend a car potty: if you go to www.amazon.com and use search word "car potty" many will come up and you can see the reviews of it. It is REAL handy, when a child has to use the bathroom, but you are in the car/in traffic/no bathroom in sight.... and it is a real life saver. My friends have them too.
On Amazon, you can read the reviews of the baby bjorn.
Good luck,
Susan