Actually, a Greatest Hits (if it's done properly) should be all the singles, PLUS fans favourites and maybe one or two rarities. It's got to appeal to "proper" fans as well as those who lyke totallee luv CLOCKZ, you know who I mean. It's a hard to get the right balance and only a few bands have managed it...
My Coldplay Greatest Hits would be (in no particular order)
1. Yellow
2. The Scientist
3. Clocks
4. Don't Panic
5. In My Place
6. God Put A Smile Upon Your Face
7. Fix You
8. Speed Of Sound (don't want to put it on but you have to really)
9. Shiver
10. Trouble
11. See You Soon
12. Politik
13. Talk
14. White Shadows
15. A unreleased track/One I Love/Careful Where You Stand/Only Superstition