Aliexpress if you want a good deal, and Amazon if you want fast shipping and easy returns. There are a lot of devices. Solid ones come from companies like Anbernic, Miyoo, Powkiddy, TrimUI, Retroid, Ayn. There’s some bad products from some of those companies too so good idea to do some research. Youtube channels that cover their products include Retro Game Corps and Techdweeb.