For a basic router, pick whatever you like the most.
No controller is perfect, but they should all be capable of handling a basic 3 axis router.
It all depends on how much capability you want at the machine, and how much money you want to spend.
Centroid is good, but unless you pay extra for the license, the conversational is limited, and you need a reasonably spec'd computer to run it.
Mach you either need an external motion controller, or run an old PC with Win7 32bit or earlier to be able to use the printer port.
I can't really comment on Flashcut as I've not looked at it for years.
LinuxCNC you are at the mercy of somebody knowledgeable about it, answering any questions you may have about it.
GRBL is limited in what it can do.
If you don't want to have a PC running the machine, then one of the DDSCV standalone controllers is a good option, however it does need all g-code loaded via a USB stick.
Personally, I run Dynomotion KFlops in my machines, but I'll admit that would be overkill for a basic router.