Word to wise, the rear shocks are easier if you have some help - someone in the trunk to help rethread the bolt and to hold a wrench while you use the ratchet.
The adjustability will be for compression (shock goes in) and rebound (shock goes out). There is no "right" - there's only a "better or best" depending on what you're asking the car to do. If you only use the car to cruise, there's no point in getting adjustable shocks at all. If you're going to drag race or do some combination of cruising, racing and spirited driving on twisty roads, then get the adjustables, so that you can tune the rear for each type of use. Me, I don't plan on doing anything except the occasional 1/8 mile drag and Camaro/Mustang/ricer kill,
so I just used plain ol' non-adjustable KYBs.