I'd make a shortlist of phones based on price and hardware, then check the XDA forums to see which of the models on that list have good AOSP-based custom ROMs available. Generally, you'll have better luck with flagship models, but there are custom ROMs available for many, many smartphones - some even get updates for longer than the official firmware.
Another option is to use adb to uninstall bloat and crapware from the official images, which can be done with varying success depending on the phone's make and model. For example, I have a Samsung Galaxy A53 and was able to uninstall or disable most of the several useless or redundant apps it came with, but several I could not get rid of without breaking needed functionality (that shouldn't depend on them, but does for some obscure and probably illegal reason).