Second Level
I got presale tickets on the second level, second row. Could have gotten floor seats but I chose not to, thanks to prices and the extra fees.
And, also, as a Phoenix resident and someone who's been to the arena for concerts in the past (floor seats once, lower level a second time), I felt like second level seats, so close to the edge of the level, might actually be better. For the seats on the floor, I was near the back, and could barely see anything. The lower level was further back and no better. My second level seats are very close to the stage, so here's hoping for a better experience!*
*And since it's Coldplay, it WILL be a better experience!