And as you say, of those, Vodafone has the worst reputation for customer service.
As an ex-vodafone customer, I'd heartily endorse this. Ironically, the only interaction I ever had with them that wasn't endlessly painful was when I terminated the service - they actually did this perfectly!
It's worth noting that over the 5+ years I was with them, their technical service (i.e. the actual broadband) was really very good - reliable and, within the limitations of my rubbish VDSL connection - consistently performant. It's just that on the few occasions where I did have to contact them, the experience was truly painful in every possible way.
I've moved away to an altnet now, but would I go back? No, probably not.