i think best host must have arena with at least 17 k. seats. wikipedia shows this:
o Belgium - Antwerp Sportpaleis Merksem - 23.000, Hasselt Ethias Arena - 21.600
o Bulgaria - Sofia Sofia National Sports Arena - 19.000
o Croatia - Zagreb Arena Zagreb - 23.000
o France - Paris Palais Omnisports de Paris-Bercy - 18.000
o Germany - Berlin O2 World - 17.000, Cologne Lanxess Arena - 20.000, Karlsruhe dm-arena - 23.000
o Greece - Athens OAKA Indoor Hall - 19.250
o Italy - Turin Olympic Arena - 18.000
o Lithuania - Kaunas Žalgiris Arena - 17.500
o Netherlands - Amsterdam Ziggo Dome - 17.000
o Norway - Oslo Telenor Arena - 25.000
o Portugal - Lisbon Pavilhão Atlântico - 20.000
o Romania - Bucharest Romexpo - 40.000
o Russia - Saint Petersburg Petersburg Sports and Concert Complex - 25.000, Moscow Olympic Stadium - 35.000
o Serbia - Belgrade Belgrade Arena - 25.000
o Spain - Barakaldo Bizkaia Arena - 18.640, Barcelona Palau Sant Jordi - 18.500
o Sweden - Gothenburg Gothenburg Convention Centre - 22.000, Stockholm Tele2 Arena - 40.000, Friends Arena - 65.000
o Switzerland - Bern Bern Arena - 17.000
o United Kingdom - London Earls Court - 19.000, The O2 - 23.000, Manchester Manchester Evening News Arena - 21.000
also there are stadiums, but arenas are better i think.
so, when you have all list, check countries financial situation, actors/singers for host, and so on. have a good day! :>