I would prefer the specialties, personally, because I'd love to watch what both of those judges do - and I suspect many owners will feel the same and will bring them quality dogs, which I would love to see!
But if you're new to dog shows, and you don't really feel like you'll know what the judge is looking for, an all-breed show with rally might be a bit more fun. Specialties are fascinating for me, but I can see where a day spent watching a ring full of dogs that all look
exactly the same may not be riveting entertainment for someone else.
At an all-breed, you can watch the Shelties... and then go check out the Afghan Hounds... and the Corgis... and all those terriers! And if you stay the whole day, you get to watch the Group competition, and cheer and clap for your favorites! And Rally is so much fun to watch.