It's a question you could answer in many ways.
For one, they all have enough know-how to know their limits.
Also, they are great song writers too.
But in pure talent? Larry has been memorable and unique, but he's not anything never seen before, and it's not like his stuff is all that hard to play. It's creative, often something I wouldn't think of on my own, but I can play most U2 songs on drums.
In a similar way, Adam is not making basslines that are really difficult.
Bono has played to his strengths with songwriting, making songs with which his voice makes sense. But overall, I can sing just like he can too. It doesn't sound the same, but it's good enough and doesn't crack or anything.
The Edge is the most talented. He has extremely thorough knowledge of the technical element and how to make a sound. His sounds are very unique, that most people cannot copy them. Some of his best songs are extremely creative too (Streets, The Fly). Overall, he is probably your most talented member.
If I remember correctly...
"Bono wants to be the guitarist, The Edge wants to drum, and Larry wants to sing. Adam wants to play bass."