The villages are generally small so there's usually not a lot to see aside from a couple of good bars & restaurants and a few shops. But that's actually a positive, because the best thing about them is sitting outside and soaking up the local atmosphere.
San Jose (Sant Josep) is quaint and has a nice bar called Raco Verde and one of my favorite restaurants El Destino. Not far from there (potentially hikeable) is Sa Tailia, the tallest mountain on the island.
Santa Ines (Sta Agnes) is beautiful to visit. As you drive up and over the surrounding hills, you descend into this gorgeous fertile farming valley, called La Corona. It's quite a sight. Nice cliffs on the coast near there too, as well as some ruins from the island's Muslim period. Also, a great family restaurant on the main street corner.
San Carlos has the hippy market once a week, so if you go on the right day you can check that out and then take a walk around.
Similarly, San Miguel has a market once a week that has locally-made arts & crafts, and a little bit of local food. I bought some amazing chorizo there. The village also has a church up on a hill that's one of the more interesting ones on the island.
Everybody loves the food in Sta Gertrudis. Several cafes there serving local delicacies with outdoor seating. This is one village I have driven through a lot but not taken the time to stop and enjoy. Definitely on my list.
You've probably seen on the relevant Ibiza-Spotlight section: http://www.ibiza-spotlight.com/villages_i.htm
Everyone's got their memories and preferences. My best advice is to just choose them at random, go take a look, and form your own