This is backwards rather than forward looking but it may be of interest.
1 - Brussels
2 - Frankfurt
3 - Eindhoven
4 - Luton
5 - Budapest
6 - Lisbon
7 - Charles De Gaulle
8 - Schiphol
9 - Nice
10 - Gatwick
Heathrow was 15th.
There is a best list; this includes a number of smaller airports, but also Dublin, Orly, Madrid, & Marseille