If you are willing to pay 200 EUR for the CPU alone, then I'd say Ryzen 2600/2600X but I'd recommend waiting for the B450 motherboards to become available if you want to spare yourself the hassle of having to jump through hoops to get the motherboard BIOS updated to support 2000-series CPUs.
If gaming is by far your primary interest, then the i5-8400 with an H370 motherboard could be a better pick as it is far less dependent on RAM frequency and latency than Ryzen, which means you get a more affordable CPU which you can pair with more affordable DDR4 without as much of a performance penalty.
If you go with the 1600(X) or 1700(X) which are heavily dependent on memory clock for performance, you'll need fast (expensive) memory to beat the i5-8400's performance in games. The 1000-series Ryzen are extremely picky about RAM, especially prior to the AGESA 1.0.0.6 update, so you may want to make sure you pick RAM specifically certified for use with first-gen Ryzen in this case or at least make certain the motherboard you receive has a BIOS with AGESA 1.0.0.6 or newer preloaded.