XL seats are the emergency exit rows. I don't know whether there is a European minimum standard, but you will get a few extra inches. Not a lot, but enough to avoid kneeing the seat in front (unless you are 7-feet tall) You also will not be allowed to put any carry-ons underneath the seat in front. (so be prepared to fight for that overhead bin space) Flight attendants are also pretty strict about not letting anybody move into those seats without paying.

Excellence seats on the left hand side of the place should have nothing in front of them. I can't recall the right hand side exactly - you might have a bulkhead or the galley.

For three hours, I would probably pay for XL, especially if you are taller than 6 foot or so.