Where is the best place for a road trip? It's an interesting question, and something I ask myself every time I look at traveling to another country now. I think certain countries are more suited towards road trips than others. Iceland - definitely a road trip country on the whole. If you want to drive more inland (on the F roads) through the Highlands though, you're ability to do so will depend on you're rental agreement as well as your skill and comfort level. Note that most rental car agencies (Hertz, etc...) give you an instant fine if you take your rental car onto one of the F roads.
Depending on whether you're traveling alone or not, and where you're going, you can save a lot by doing a road trip through the country. It does depend a lot on your travel style though. If you're traveling solo and planning a private tour with driver, than just renting a car and driving yourself is likely to be cheaper.
If you're joining a group tour where there's 14-20 people on a bus (or more, but don't do more, that ruins the experience), then it's possible the group tour option will work out cheaper. Either way, I really like the idea these days of just driving myself around when possible. It lets me stop whenever I want and grab a photo like this one. You're more in control of your destiny, for better or worse.
I say, drive yourself around if possible because, frankly, sometimes it's just not realistic or not worth it. If you don't know how to change a flat tire, don't even think about doing a road trip on unpaved roads in a country where your mobile phone can't always pick up a signal. Iceland, Faroe Islands, and other European countries though - you're bound to have plenty of paved roads with decent cellular service.
Ever since my road trip through Namibia a few years ago, I've been aching to go back to another road-trip friendly African country. Being able to drive yourself around, give yourself your own safari ride, and see a new country is a truly life changing experience.