I think they are about the same. The thing is, Where The Streets Have No Name sounds like tons of other U2 guitar parts. Wanted Dead or Alive has a riff that was like nothing at the time: full blown acoustic. Same with Prayer. I would be willing to argue that Prayer has a more distinct and recognizable riff than Wanted. It's talkbox, it's different, not to mention it was a massive hit. Play most anybody that talkbox riff, and people will be thinking "Bon Jovi" right away.