I'm fairly brand agnostic, but American tends to be my usual carrier. Coach on a 3x3 is annoying, though the seat updates do aid with knee room, which is most important to me. I will not pay for extra space or an exit row, though most flights I take give me at least the exit rows free with the status I carry.
I'm maybe 25% successful on upgrades (free). They're marginally useful, as the space and ability to work or nap is much better. Not sure the food/drink is worth it, Ive gotten tired of repetitive menus on domestic first.
Ive flown first class internationally once. Traded in miles to do so. The food was nice, the sleep was better. Id rate coach food and drink on a nice international airline like Turkish Air to be better than a domestic carrier's international first, but Ive certainly not seen it all...