AA does not have unlimited domestic upgrades, you will get a certain number of stickers - I think 4 per 10,000 miles flown, each good for upgrading 500 miles of trip. Now, if you think you might never ever get upgraded on US as a silver, at least AA would provide something guaranteed. But my personal experience on upgrades over the years on US has been very good. A few years ago I got a free trial silver and while on that I got several upgrades, and the following year I flew very little but at the end of the year my girlfriend (no status) and I got upgraded LAS-PHL. (Admittedly it was Christmas Eve, hardly a big travel deal for elites.)

I think all FF programs give you a free checked bag as silver.

US also has a somewhat unique program that allows you to buy segments for a higher status. They aren't cheap, but if you fly 45 segments and want to buy gold for the next year, 12-18 segments are $789. If you feel like that will get you (say) 10 more upgrades the following year, it's like paying $79 per upgraded segment.

I'm gold on US and I think the benefits are pretty good. And as I said, I wasn't unhappy as silver.