I did the distance groundschool with Atlantic and on the whole, I was very pleased. They were very flexible in working around my personal needs (in terms of re-structuring modules, fitting in brush-ups etc.) and we're generally very responsive when questions (often!) arose.
I started with them not long after the Jep. notes were first released, and whilst there were a few errors in them, I (and my physics/science teaching better half) found them to be of a good standard. And, whilst hard-back books aren't the easiest to work from, they do look nice now with all my other stuff on the bookshelf! Plus, they supplied the whole course in PDF format so I could work off my laptop.
And, I ended up with an 87% average with only one exam re-sit, which for a thicko like me, was very satisfying!