I don't understand why "New Years Day" isn't considered a warhorse? It was pretty much their first real hit song, the one that actually got them on the map. I still hear it from time to time on classic rock radio, and in random places like restaurants or malls, etc. U2 seem to prefer not to play it, but seem to understand that sometimes it is needed. I think it's one of the better songs of their "warhorses". It's a good audience singalong, and the crowd really gets a kick out of Edge doing triple duty (guitar, keyboards, backing vocals). I'll break it down for ya, as I have time.
LoveTown Tour- NYD started missing shows occasionally. It was starting to be seen as despensible here.
Zoo TV- Missed the entire first 2 legs of the tour, in arenas. Only was brought out when the show moved to stadiums, and WGRYWH was replaced by NYD to beef up the setlist a little. Was played nightly afterwards.
Popmart- Wasn't added until late in the first leg. Some of the Pop songs weren't working live and were dropped, and they needed to add something from their A-list to, once again, beef up the setlist. Was played nightly afterwards.
Elevation- Was almost a nightly staple, occasionally rotated with Mysterious Ways or Discotheque.
Vertigo- Played quite a bit in the early part of the tour, then at most of the stadium shows. Wasn't played at all on the fall North America leg, despite having 50+ shows. Played at roughly half the shows.
360- Played 29 times out of 110 shows. No method to it, really. Sometimes it'd just pop up.
I&E- Played 3 (wtf?) times out of 76 shows.