Dog shampoo itchy dry skin ?

I have a 9yr old pitbull with skin allergies, it was never determined what her allergy was, but it has been being controlled by daily Benadryl per the vet, but she still can get itchy and now being winter her skin is very dry, I've been using Hypo allergenic Oatmeal shampoo on her and Resincort lotion on her after but she's still very dry, and I just adopted a corgi who is also very itchy! Not as dry but I did notice even when I saw him at the shelter he was itchy (no fleas or mites) and he's been licking his paws alot (Im going to ume he has some sort of allergy too!!! He has a vet appointment on tuesday) The oatmeal shampoo doesn't seem to be working any miracles on him either, I actually work at the vet in the grooming department, and theres three medicated shampoo's that im looking at to get for the two of them, and was just wondering on other peoples opinion's on which shampoo out of the three would be the best for the itchy's and dry skin, There's Dermal-Soothe, Relief, and Epi Soothe, any opinions?