I'm in the Ragstone camp for the A4 and A3 classes, Hobby Horse may be good for other locomotives but for those two classes the few bits I got from them are still in the bag, mainly parts for the chassis, parts for the cab etc I cannot comment on. Both are pretty much equal in quality and some of the Ragstone brass parts are very nice.
No affiliation, just a happy returning customer.
Laurie also does good work, but no idea what he has in his range for the A4 or LNER Pacifics.
In short, you won't be upset by the quality of parts from any of them