The best warriors in Europe during the Middle Ages were likely the Swiss Pikemen. They dominated battlefields in Europe for several generations. Consider the tiny nation of Switzerland pretty much curbstomped the Austrian Empire and sent single survivors back, on more than one occasion, to "tell the tale".
The Polish "Flying Hussars" are pretty famous. They were heavy cavalry, and elite.
Germany is actually a very new country, less than 200 years old. But large swaths of central/baltic coast was dominated by the famous Teutonic Knights.
I don't know much about Croatia, but England's most famous warriors were probably their Longbowmen.
In England, we still have today the Yeomen Guard - or, as they are more commonly known - the Beefeaters. They are a mostly ceremonial unit nowadays, but still patrol the Tower of London.
They were, however, established at a time of great war in our country. Henry VII had just won the throne, ending the Wars of the Roses, and seen the dangers of a poorly protected Royal fortress. So he established the order to keep an eye on the prisoners, and generally keep order within the vast confines of the Tower of London.
England you would start with Gedriht who were the early proffesional class of warriors, and were the personal household troops of a warlord. Then there was the Duguth and Geoguth who were older experienced fighters and the “youth”, young warriors. These were probably part timers who had other trades and occupations when not needed.
Later on the Gedriht have morphed... their leaders have become Thegns and the others become Huscarls or Housecarls, personal bodyguards and full time warriors. The Fryd was a militia, the select Fryd served for a while and were well equipped. The greater Fryd were called up when needed and were not always well equipped
I'm assuming you don't mean those specific countries, but European countries in general.
In that case, there were the Serbian Hussars (not to be confused with Polish Winged Hussars) who were mercenaries operating in Poland and Hungary, where they ended up fleeing the Ottoman invasion. The word "Hussar" comes from the Serbian "Gusar", which is equivalent to the word corsaire (pirate, privateer). Here's what these warriors looked like:
User Stronium90 mentioned the Swiss Pikemen. Here are some images of them if you're interested (they're still around today!).
Besides these, I would look into the free companies of the high middle ages (hired mercenaries that often acted as bandits). Hope I helped.
I believe they were heavily involved in the 30 years' war. They were extremely brutal in their actions, often engaging in pillaging and lynching, that it sort became a motto to say "God, save us from plague and Croats!", which I find pretty interesting.
The slogan "God, save us from Plague, War, and Croats." (Gott, behutte uns von Pesten, Krieger und Kroaten.) stood before the cathedral in Magdeburg until WWII when it was taken down by the Nazi regime.