Location. I don't know the two areas but you do! Look at (lack of) facilities, neighbours, general area, schools.
You've said your DS would either have to travel with you or use the school transport provided. Being realistic, which of those works best for you. Would having to pick him up and drop him off every day be doable for you? Would he be happy using the school transport? Would lack of a regular bus service interfere with him being able to travel alone or is that not an issue?
Visit at different times to get a feel for the places. You might find you'd have a very noisy neighbour.
As for the houses, look at how you would use the space. Would a dining-kitchen be easier than a separate kitchen and dining room? Do they both have a second loo? Does the 'attic storage room' (they're not allowed to call it a bedroom so it doesn't meet regs or they haven't applied) give you needed separate space? How do you get to it (I've been to see one house where there was just a ladder!) Does the other house have the option of adult only space?