I would say that Europe is one of the most diverse continents in the world. It offers something for everyone, young/old, female/male, backpacker/luxury travels and culture/fun. The culture in every country is fascinating and full of interesting history. Also, you can visit the mountains, small and big cities and the sea.
When to Visit
Ok- the US do not have a best time to visit. It really depends on what you are looking for. New York for example is beautiful during Christmas while Los Angeles is best to visit during summer. While I suggest to visit Hawaii rather towards fall.
What to Expect
Northern Europe which is known for its expensive lifestyle so cheap backpacking can be difficult as you will be forced to spend a minimum amount of money. It is known for its beautiful nature landscapes with the Northern lights for example. Every country (like Denmark, United Kingdom, Norway, Iceland,...) has its own currency.
Eastern Europe which is well known amongst the budget traveller as these countries (like Czech Republic, Poland, Slovakia, ...) are much cheaper than the rest of Europe. It is also a great cultural experience destination.
Southern Europe consists of countries like Italy, Greece, Croatia and Spain. This is where you will find the most sun. Who doesn't like to eat an ice cream on the beach boulevard? The beauty of this part of Europe is mostly during summer. It is a mix between budget and luxury travel.
Western Europe is also more an expensive travel part of Europe. However, you can definitely find cheap places to stay. Countries of Western Europe are for example France, Germany and Switzerland. Here you have a mixture of beautiful cities, beaches and mountains.