This is my personal best-of list—everyone has different preferences, but mine is based on the view of IllumiNations, how close you are, potential for smoke (though with shifting winds, there's never a guarantee) and lack of trees obstructing the view:
1) Italy Isola/Italy Isola West
2) UK Lochside
3) UK Pubside (max 10 guests)
3) Terrace des Fleurs (France Upper)
4) Eau de France (France Lower Terrace)
5) Mexico Vista (if you can get it—they usually reserve it for parties of 75-100)
I am not crazy about UK Terrace because of the fixed umbrellas, and Rue de Paris (French Island Arm) is quite far from the show, with more of the island obscuring the view than you get at the other two France locations.
You can see photos of the view from each of these spots here:
http://disneytravelbabble.com/disney-weddings/wdw-venue-photos/#epcot
Depending on your guest count, they may tell you your group is too small to use certain venues, but you can keep checking back, and if no larger group has booked the space by about 30 days out, they will move you there.