In my experience, there are interesting things to see and do, good food and nice people just about anywhere you might go. I've visited most of the countries in Europe and have never been anywhere that I wouldn't gladly go back to visit again. What's best for you really depends on your interests and expectations and to some extent on when you go if you're interested in local festivals or special events. At this time of year, I particularly like the Netherlands since the tulips will be coming into their peak and the King's Day holiday will be coming up at the end of the month.
I spent over 13 years living in Mirandola, Italy and loved it there. I can highly recommend Italy - beautiful art, architecture, scenery and music, interesting local festivals, great people and food. Beaches, mountains, lakes, the ocean, historic sites, world class museums and galleries and a lot of varied things to see and do. The best part is the wonderful Italian people.
Well a lot depends on what you are into.
Getting on one of the popular hiking trails in Spain and Italy is great for hikers. Walking gives you something to do during the day and you will meet other people on the trail and often make friends with people at your pace.
Self-travelling can be great depending on your personality. You can take up a hobby like photography and have a goals of places to go and photograph.
If you are into partying find the backpacking scene and party with other travellers.
This would mean heading to the south where the weather is good and the prices are cheap (Spain, Greece, Italy) but there are hostels everywhere.
What are you looking for? Culture? Sights? Beaches?
Beaches - Greek islands (especially Zante, Skiathos, but also many others e.g. Crete).
Culture and sights - Berlin, Athens, Barcelona, Prague.
Both beaches and culture: Rhodes island (Greece), the Rhodes city centre is amazing.
Good food - Italy, Greece, Spain, France.
You could also do a tour with two countries, e.g. Italy & Greece (connected by plane and ferry) or Belgium & Netherlands (connected by bus and train).
Generally speaking, in Southern Europe prices are cheaper (Greece and Spain, especially; Italy is not that cheap, on the contrary Rome, Florence and Venice are very expensive).
Maybe a couple of websites (national tourism organisations websites) will help you decide:
Greece - http://www.visitgreece.gr/
Spain - http://www.spain.info/
Cyprus - http://www.visitcyprus.com/
Portugal - http://www.visitportugal.com/
Germany - http://www.germany.travel/
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