Another Northumberland fan. It has some of the most beautiful beaches, loads of history, fantastic historic houses, great countryside. Just a shame it's at least a 6 hour drive from where I live.
We have so much unspoilt countryside in this country, and most of it very accessible. Our national parks are just fantastic. Nowhere is more than about 70 miles from the sea, and you don't have to go far off the beaten track to find quiet beaches in most areas.
We also have lots of interesting small towns and lovely villages, it's easy to get a decent meal out a reasonable price in pubs, bigger towns will usually have a museum and gallery or two so there are things to do if the weather is shite.
If you go to somewhere like Dorset, you'll get the best of everything. Lively Bournemouth and Poole for cinemas and stuff (although Wareham has a delightful, tiny cinema that is like stepping back in time), unspoilt beaches on Studland (well, the whole of Purbeck, really), some lovely small towns (Bridport and Beaminster are my favourites), fantastic countryside for walking or picnics, nature reserves, Brownsea island, New Forest on the eastern edge, beautiful Corfe Castle, Cranborne Chase, ancient sites all over the place, including the eerily beautiful Maiden Castle.
If I was condemned to spend the rest of my life in just one county, I'd probably choose Dorset.