Can you recommend a good CPU for around 100 to 150 euros for gaming that will last for some years? I know Ryzen is great but a store near me also has an i5 9600KF and an i510400 for around 140 euros. Keep in mind that I live in Europe so maybe link amazon de or italy. Thanks!
As sizzling wrote already, I would wait for Ryzen 5xxx series launch.
Also, the sockets for 9th and 10th gen intel are not the same. Do you have any kind of compatible motherboard and RAM for any of those two CPUs?
Is it $150 for the CPU alone, or are you planing on changing motherboard and perhaps RAM too?
And finally, If I have to choose a gaming or productivity cpu right now between those two CPUs (9600K and 10400) I would definitely pick the 10400, as it has 6 cores and 12 threads and you will want those extra threads for actual and future games, or if you do some content creation, code compiling, etc.
Keep in mind the 9th gen platform is dead, so the only reason to buy 9th gen CPUs right now is if you already own a compatible motherboard.