I must confess I've not had a 'worst' tent. Some have obviously been more suited to my camping than others, some have been better quality than others, but none have let me down or been disastrous. That said, I've not had that many tents.
Anything with 'Eurohike' printed on the side. Didn't learn my lesson after tent one and, n a moment of madness, bought another - that was rubbish as well.
I'll admit that the above was a few years ago but refuse to believe that they have improved that much.