I second what Blacky has said with it depending what kind of traveller you are & skipping paid tours. They're very fixed & you're stuck with whoever is on the bus. I personally haven't done the jump on jump off but that does give you much more flexibility. I tend do spend more time doing less .....if you want to see all the main sites either of the options above would work. If you want to be able to wander a bit, find out the fabulous, but a little off the tourist trail options, have the flexibility to stay an extra week cos you're sick of moving or just love where you are then flexibility is key.
At 25 I spent 3 months working in a pub in Edinburgh (TERRIBLE pay!!) then found a pal, bought a pushy & spent 3 months cycling through France, Belgium, Netherlands, Luxembourg, Germany, Italy & back into France. We linked a couple of sections with trains. I loved travelling that way and met so many people I would otherwise not have met. In 3 months we paid for camping only twice, either camping wild or with people along the way. Amazing experience. Till my buddy's bike got stolen then it all went a bit pear shaped, but anyway!
Train travel in Europe is easy & that's another option you could consider. There used to be train passes you could buy, I'm guessing they're still available which are pretty economical and a good way to cover lots of ground & still see some of the scenery. Will have a think about my top 5 places in Europe