U2 concert at Soldier Field?

What are good tickets for the U2 concert? I've never been to a concert before and I'm not sure about the seats. Are Floor GA seats any good? And what about the Lower seats, sections 148-154, why are those seats so much cheaper than others? Are they looking at the back of the stage or something? I'm looking to spend around $100-$115 if you have any seat suggestions. Here's the link to the site: http://www.stubhub.com/u2-tickets/u2-chicago-soldier-field-7-6-2010-906478/?isGen2Event=1