I am planning on buying a budget gaming pc and I am going to buy the Ryzen 2400G and only use its integrated graphics, no GPU. I am not sure whether I should use 16GB(2x8) 2400mhz Ram or 8GB(2x4) 3000mhz. I know that Ryzen CPUs greatly benefit from faster memory, but is it still better than 16GB of 2400mhz ram?
You probably do want 16gb, if you are gaming on the integrated vega gpu reviews have shown 2933 mhz ram is the sweet spot price / performance. The performance scales nicely from 2400 -> 2666 and from 2666 -> 2933, however after 2933 the gains are small (1 to 2 fps).
That said, quite a lot of good ram kits will overclock, so you might be able to bump up the clocks on that 2400 mhz kit to 2933 (I was able to do that on my machine, which is based on a B350 mobo and R5 1600).