tbf it depends on the options, if it's a band too big to play anywhere better then arena is usually better than outdoors (which is a lot of fun if it's sunny with a load of friends but always hit and miss soundwise). if it's a band you expected to see in a slightly smaller theatre then arenas are usually a bit shite, but i did see QOTSA in an arena a few years ago so no big surprise.
also, was in the arena in Dublin last night for somehow the first time ever for Radiohead and it's surprisingly decent for what it is. really good layout, feels like a huge version of the Roundhouse and doesn't feel that massive compared to the more sports stadium-layout of the Belfast one or the O2. would actually be quite happy to see more gigs there