Euro away games are without doubt the best. In fact I rekon the europa league makes them as good as they are.
Champions league, getting all the biggest teams in the countries Milans, Madrid, Barca, Bayern, Lyon etc wil imo get boring also I imagine the tickets are more expensive.
Europa League offers cheaper tickets to more obscure locations against teams that are not the most popular in there leagues, I think its ace.
Done Salzburg, Poznan, Turin & Aris and for me Turin was the worst trip although we were playing the mighty (cough) Juve.
Gutted tho as gonna have to give Kiev a miss should we beat Aris as the quarter final, semi final and final (should we progress) will cost me a bomb, also season ticket will need to be paid for around that time aswell.
But if you can afford it get on any of them, they are all quality.