The Ryzen APU’s work by sharing RAM with your system and using it as VRAM, so to speak. 4GB of RAM is barely enough to run a basic system with Windows 10 and games and other programs. So using only 4GB with an APU as a gaming machine will yield pretty bad results no matter which processor you went with.
My advice would be to either wait until you’ve saved enough to get 8GB with the Ryzen 5 APU or, if you NEED a system right now and NEED to game on it immediately then the Ryzen 3 with 8GB of RAM is the better option. You can always wait to sell that processor and snag a newer one for the AM4 socket.
Notice how I emphasized NEED? If you can wait then do that. Don’t spend money because you have just enough to do either one. That’s a waste of money, in my opinion. Just save the extra money and wait to get the best you can. But it’s your money and what you do with it is up to you.