If you're in SW Pa., you won't go wrong ordering trees from Adams County Nursery, ( ACN ), in south-central Pa. They're on Penn State's list of highly recommended nurseries for fruit trees that has nurseries from a number of states on it. I've ordered apple trees from ACN for our hunting camp and every tree was great - very nice stock. Cummins is also a very good nursery out of Ithaca, N.Y. Our camp has bought lots of trees from them too with no problems at all. There are good nurseries from all around the country, but those are 2 that are from the same relative "neighborhood" - climate-wise - as your location. Call ACN and Cummins to have them send you their catalogs. ACN has experts there who you can talk to ( I have ) that can answer any questions you have about varieties. If you give them your location, they can suggest several varieties & rootstocks that would work for you. Nice people there at ACN, and they're the closest
GREAT nursery to your location. All the trees I've gotten from ACN have been 3/4" to 1" trunk dia. and had a number of branches already ( that's called "feathered" ).
From all I've learned from others on here, nursery owners, Penn State's head of fruit tree breeding program, and several universities' written studies - a couple good bets for disease resistance and ease for home growers are : Liberty, Enterprise, Galarina, Sundance, Winecrisp, Nova Spy, and Priscilla. These are all regular apples - not crab apples. These have all been bred for disease resistance so growers could cut back or eliminate spraying for the major apple diseases. I'm no expert, but I ask questions and seek as much info from the real experts as I can get my hands on.
The rootstock that your trees are grafted onto will determine how big the trees get and what diseases / conditions they will tolerate & resist. For most of the soils in Pa., Penn State recommended to me to go with MM-111 rootstock. It'll grow a tree about 16 to 18 ft. tall, and MM-111 is well-anchored, ( doesn't need staking for support ), resists wooly apple aphids, & tolerates heavier, poorly drained soil. You can read about apple rootstocks online. I'll come back here with a couple links.
Back. Links to rootstock info : www.goodfruit.com/wp-content/uploads/appleRootstock-Feb12016webPullout.pdf
www.orangepippintrees.com/articles/fruit-tree-advice/rootstocks-for-apple-trees
Do yourself a favor and research some of the varieties listed above and basic apple tree care as well. Knowing how to plant, protect, prune and train your apple trees will save you headaches. A good resource is Penn State's publication - " Fruit Production For The Home Gardener ". I have it and it covers many fruits - not just apples. It runs about $12 and is worth every penny. It's not so heavy-scientific that the avg. person can't understand it. Hope this helps.