When I travel, I rarely rent cars. Driving is a hassle in many countries. Driving is exceptionally dangerous in others. For me, relying on public transportation has always been my go-to method for foreign travel.
With that said, I realize some of my readers would rather have the freedom associated with renting their own cars on vacation. If you are moving around a lot on your holiday, it may be more convenient to drive yourself.
I found this article to be exceptionally valuable. It covers all aspects of European car rental. Most of the tips are also useful for other continents as well. If you are considering renting a car in a foreign country, it will be a useful resources.