If you haven't traveled very much before, you may want to consider a tour. They are not right for everyone (personally I prefer traveling on my own and setting my own schedule and itinerary) but if you are very new to traveling and don't have a clear idea of what you want to see, a tour might be a good way of seeing a few highlights, then you can come back on your next trip to spend more time in the places you really enjoyed. A tour price should fit your budget (which I wouldn't really consider "budget travel", but anyway )

Some other things to think about:

-what time of year are you traveling? If it's in the next few months, Northern Europe will be rather cold, and may not have the best weather for touring around.

-are you interested in seeing museums? historical sites? beaches? shopping? hiking outdoorsy stuff? By figuring out what you want to do, you'll be in a better position to determine which countries/cities should be a priority.