Define “Europe” and what are your interests?
Prague is great but may be a little out of the way. Myself, I like history and interesting geology, so the Dordogne Valley of the Aquitaine region is great, nice climate too. That says Sarlat for a city, but admittedly very few people would name Sarlat for a first European visit/tour.
Funny that you should say that. My first time to France was to visit a friend who lived in Salignac, just 10 miles away.
-PJ