Hi Clearprop
As the former designer of all Bristol's learning software since it first started using it and as an author of several ATPL manuals I think I can add something to this thread!
Both Bristol and Oxford provide very good DL materials and you would not go far wrong in choosing either of them. However they are not the only game in town. There are some very good smaller schools which arguably might be able to offer you a more intimate teaching experience and a solution which is more closely tailored to your learning style.
Equally there are some really poor operators out there who make up for the lack of comprehensive teaching material by heavy reliance on exam databases.
Unfortunately too many DL students have fallen into the trap of thinking that passing the exams by hook or crook is all that matters. In consequence some have spent rather too much time learning exam answers rather than learning the underlying concepts. The result has been a much increased failure rate in type rating courses. In the words of one very experienced training captain "they just don't seem to have any basic understanding anymore".
At times, when ploughing through some of the more obviously esoteric and irrelevant stuff, it can become very tempting to ditch trying to understand and instead go for the quick kill (aka AtpOnline). I urge you not to fall into this trap.
Whichever school you choose, set yourself a realistic timetable based on the number of hours you can reasonably expect to devote to study each day. The emphasis is on realistic. If you set yourself too high a target you're likely to fall behind and become disheartened. Allow extra time for going back through previous material to make sure you keep it in memory.
When you open the very first book on the first day it will seem like you have an impossible mountain to climb. I certainly felt like that when I began. But if you just keep plugging at it you'll get there.
As for which school to use. I suggest you sign onto their own forums and ask their students directly.