Stop with the pictures you're making me homesick!!!
Avoid Jersey, too many Bergerac wannabee's.
Biased but Guernsey's museums are better, Fort Grey (Cup and Saucer) really worth a visit for some Pirate/Shipwreck History, Castle Cornet has some great history. The Guernsey Museum. German tunnels at La Vallette, Occupation Museum, Underground Hospital, some restored German bunkers on the South Coast, Amazing cliff walks. Beaches are pretty good too.
The Town sea front is much prettier than Jersey and there's some cracking restaurants.
Definetly also consider a day trip to Herm or an overnight stay in Sark.