For me in between Frederick and Hagerstown it’s Hafers as the best with great customer service. Shopped with them since they were in the basement. Gun Center on Rosemont as the worst. Bad customer service, act like they’re doing you a favor in showing you a gun. Antietam Firearms in Funkstown is also good to deal with.
Hafers in Hagerstown is a great place but too far to drive for me to go there often. Tyler's in Halthorpe is great and Chuck is a stand up guy.
+1 on Hafer's. I've never had a bad experience there and the customer service is easily among the best out there.