CATS
I recently completed the CATS distance learning course, passed last 3 ATPL's in April 2014. Here is my summary:
Material: Thorough, if you are good at learning from books then you will have no problem. Would possibly suggest supplementing a couple subjects with the oxford cd roms, for me I got the ones for Meteorology and GNAV, helped enormously.
Ground School: Great for distance learning, 3 x 1 week brush ups, really just spent doing exam papers and going over things you are unsure of. Would advise making sure exam ready before attending. Instructors were good and they sometimes bring guest instructors for particular subjects.
Overall: Great for what I needed, very much DIY course, but if you have the aptitude, you should have no problem. If you need spoon feeding, then do a full time course. I got 92% as an average, so it's possible to do well with them.
I would also get a year subscription to Bristol Question Bank no matter who you go through. A LOT of questions from there came up in the exams. Ops procedures was almost like going through the question bank.