For emulation and overall gaming I would choose phones with Snapdragon chip. For now it's the best/most compatible/fastest option.
Emulation on Android
Thanks, I will take that into consideration. I've been looking for used devices and I've seen a few Huawei (like the P30 Pro) that have "Kirin" chipset, do you think it's a good idea to get that device? From what I've seen in general it's a good phone but I'm afraid of losing emulator compatibility because of the chipset.
For(immediate) compatibility only snapdragon or you'll have to wait longer for other chips to get support. Snapdragon is the most popular right now so everyone works with it first. Edit: I can't suggest any particular model, I've been out of mobile gaming(and overall mobile tech) for a few years. You can learn a lot on youtube. I was dreaming of buying Pocophone, it was the best(relatively cheap but also high end) like 3 years ago(not only for gaming).