Time for an update on this topic. Emulating current generation consoles is either still in the very early stages or not really possible yet (depending on the console). So if some site claims to have a fully working and playable PS4, Xbox One or Nintendo Switch emulator, it is a scam so avoid them.
Progress on Wii U, PS3 and 3DS emulators is advancing but don't expect many games to be fully playable at the moment. Progress on Xbox (original) and Xbox 360 emulators is slow.
Emulation can be hit or miss when it comes to how well supported a console is, so if in doubt ask on our forum or places like /r/emulation.