Apple TV doesn’t have ads at all. If that’s all you care about, I would say go for that.
The Firestick isn’t really jailbreakable per se, but it doesn’t really need to be. You can sideload things with extreme ease. There’s a pretty decent app that allows you to watch YouTube with no ads or sponsored content shown. That alone is worth the cost of a Firestick for me. It does have some ads in the menu, but they’re not super obtrusive and never bothered me much. Plus the cost is much lower. You used to be able to put a different launcher on the Firestick and never see any Amazon content at all (ads) but they fixed that a while back and I haven’t bothered to see if that works again, but for all I know it might.