Optimum seats for a concert?

Depends on the venue. In many cases I think you are right. But a few halls have better acoustics at the mezz or balcony level. Pittsburgh is definitely best in the balcony. Baltimore--well it changes every year as they change the acoustics--haven't sat in the balcony or mezz yet this year. The floor has some anomolies with delays coming off the new ceiling--they mezz is probably better as the delays won't be as long compared to the direct sound.
Center in my opinion always sounds best--sometimes slightly stage side right--if it's a piano--I like to see the keys.

Abstract7: For sound as the only consideration in the Meyerhoff in Baltimore, the best seats are high in the back (Terrace D and Center). These are also the cheapest seats. The sound is balanced with a wide sound stage field. Terrace C is good too. You just have to not be bothered by being up high.

I sit in an upper box over the stage on the left. I guess this is near field listening in audiophile terms. But I like to watch. With pianists I look right down on the keys and can see everything. The sound is very clear there, because it basically comes straight up.

Sugarbrie--thanks for the input. I had not previously even had that suggestion--and I know quite a lot of people that go regularly and move around to try different acoustics--including some in the orchestra that don't have to play every piece. I will have to try the Terrace.