I know we like to debate about which songs are best, but I think one of the best ways is to see which U2 song is most played in your media player. If you have a media player that records the number of times each song is played, then this is really easy. If not, then you just have to be honest with yourselves. If you really want to, you can break it down to album versions and live versions since I know there's a big difference between the two.
Album songs:
1) Mercy (not live version): 131 plays
2) Smile: 120 plays
3) With Or Without You: 93 plays
Live:
1) The Fly (Vertigo Tour live from Chicago): 61 plays
2) Where The Streets Have No Name (Elevation Tour live from Slane Castle): 54 plays
3) City Of Blinding Lights (Vertigo Tour live from Chicago): 50 plays
I think these songs actually reflect my personality quite well, explaining why I constantly go back to them.
There are 9 U2 songs in my Top 25 Most Played list on iTunes:
01. Get On Your Boots (271)
08. Elevation (140)
10. I'll Go Crazy If I Don't Go Crazy Tonight (Live U2360 Remix) (122)
12. Magnificent (119)
14. Vertigo (118)
17. Breathe (115)
19. Even Better Than The Real Thing (110)
20. Mysterious Ways (110)
24. No Line On The Horizon (102)
1. Return of the Stringray Guitar (99 times) I was at that show, and I will never forget what I saw at that moment: U2 for the first time in my life!
2. Get On Your Boots (94) Live from the Rose Bowl
3. Discotheque (78) Popmart
My most listen album songs:
1. I'll go crazy if I don't go crazy tonight
2. The Wanderer
3. When I look at the world