In my experience you don't get much in the way of 'proactive upgrades' like you do in Europe, though maybe they would if you asked.
The flip side is that American airport locations are more amenable to you switching cars for other available options, if you're biased towards a brand, or provide cars that are available for 'paid upgrades' at good prices.

The other key European perk is the 'free second driver' - this has received confused resistance from the agents when I've asked for it, but then when I've insisted that it should be free, they've ended up being able to do it - maybe it comes up as no-cost on their screen or something. So just insist on it if you're trying to do that.

US stations are also good at 'pre-clearing' your documents and putting your name up on the screen, which is always fun. And that seems to go smoothly despite being from overseas.