We had the exact same issue with Liebling. He would be fine with no pants, even use the potty/loo occasionally, but pants were a nightmare. He preferred nappies and would ask for one when he wanted to do something.

I asked him if he wanted pants or nappy, he said nappy. I went with that and didn't stress. He knows himself best - why persist with something he's not ready for? Will you do that when he's old enough to drive and can't control his car? Anyways, Liebling saw his best mate using our loo a few months later and pants all the way - although it took him another 4-5 months to consistantly not poo in his pants, although he knew when one was coming (he could ask for a nappy for a poo, which got rid of all the disposable nappies my mother kept buying me because 3 years in I still didn't really want to do cloth).