I think both aircraft would be excellent additions to the armoury, although my personal preference would have to be the F-35 - mainly due to my love of carrier landings.
Speaking of which, there is an add-on for FSX, containing the Harrier, Rafale, & Lightning II. The add-on is carrier-based, and I beleive the harrier has a hover option because it's allied to the British carriers, which means it has to be able to hover in order to land. It's called Carrier Strike Force, go check it out: