In my signature below there's a video from my ride across France last year. It was across the south, whereas in the past I've been across the lower north of France. Both were good rides, it's all about the quiet country roads and great food. I went back to France because it's just such a nice place to be. Got a bit sick of the French this time, but I forgive them
I once did a four-month W-shaped tour across Europe from the Netherlands to Poland, as far north as Amsterdam and Warsaw, and as far south as Geneva (Switzerland) and Timisoara (Romania). Netherlands/Belgium is over in a flash because it's flat and there are entire roads dedicated to bicycles, but it's an experience.
There was good cycling in Germany, Austria and Hungary. One major part of my trip was following the Danube through Bavaria, Austria, Slovakia and Hungary, where there are cycleways alongside it the whole way and lots of amazing, history-buff things to see and do (and drinK).
If you like hills, go to Scotland. I've been around it on a bike and the combined total of elevation you gain is supposed to be comparable to scaling Everest or something. Also northwest Scotland can be more beautiful than anywhere in the world.
The wildcard I would throw in is Switzerland. People think "holy crap, it's all mountains", but it's not - you can ride the whole length of Switzerland along scenic lakes, with the Alps on one side and the Jura on the other. Suggested route: Geneva to Schaffhausen, then get a train somewhere. It's amazing, safe, cultural, and expensive (the only downside).
Having done my return trip to France, the place I would personally head for is Germany because I speak the language and I would like to see the parts I've never been to. I plan to ride all the way around Germany next time I can afford to travel to Europe.
I've never done a bus tour, but a Kon-Tiki tour group camped next to me one night in Budapest and they were bloody awful. They had not smelled the smells of country roads, sat under a remote tree with camembert, baguette and vin rouge, then ridden drunkenly onwards in the rain, and they hadn't really survived anything significant. They didn't get lonely, I suppose, but neither did I when they chatted to me all night.
If I can answer any questions about these places, fire away.