A lot has been written lately on the transportation options available to European travelers. Low-cost carriers, such as RyanAir and EasyJet, have made air travel a serious option when hopping between European countries. Others are touting the freedom of renting a car and letting adventure take you where it may. Call me old school, but personally, I'm still stuck on the Eurail system.
Yes, the airlines are super beneficial when your destinations are as far apart as, say, London and Athens or Madrid and Budapest. But if you're simply traveling around Europe, part of the fun is actually seeing the countryside. Flights are certainly efficient, but they can't offer the same atmosphere as the trains.
As for hiring a rental car, this definitely gives you flexibility not afforded to you by train or plane. However, how many languages do you know? How about the rules of the road ... in Germany ... and then France ... and then Italy? Yes, it can be a bit unnerving - and I know this from way too much personal experience - driving around foreign countries, trying to figure out the Dutch word for "exit." My traveling companion and I learned the hard way that "ferme" means "closed" in French.
Plus, what kind of driver's license do you need? And what about insurance? Road maps? And have you seen how much gas is in Europe!? Then, there's the issue of parking, and trust me when I say "issue." Taking a rental car or another auto does allow you to venture off the beaten path, but with that freedom comes a bevy of other things to consider.
The trains, on the other hand, are efficient, relatively easy to navigate and, while not cheap, they offer a pretty good deal. For me, the lack of stress was worth the cost of the ticket every time.