BabyBjorn! Especially if you have a boy. It is high enough on the front that DS can pee in it safely (without outside spills!), plus it is nice and high in the back as well, making it really comfy. We also use a BabyBjorn insert for the toilet. Love that as well. I'm allergic to seats obnoxiously covered in characters.
Re: can anyone recommend a potty?
That's a great one, especially for little boys (high splash guard).
Just bought this one and it works great. It has a nice large oval bowl.