Speyside should be a good option e.g. for forest birds, grouse, raptors etc. Might be a bit early for some things (e.g. Dotterel) but the same would be true wherever you go. Also, in Speyside you're near the Moray coast where at that time of year you should have a good chance for White-billed Diver (around Portsoy), as well as other divers, Black Guillemot etc.
Other good places at that time of year would be Mull or Islay, but it depends what you want to see.