Which cog type does flip-flop hub take?
 

If I was to want to change the cog on a flip-flop hub (fixed side, not free-wheel), what type would I use?

Threaded:
https://cimg9.ibsrv.net/gimg/bikefor...dfc40a6b66.jpg

Or unthreaded:

https://cimg6.ibsrv.net/gimg/bikefor...0525435bad.jpg

I don't have a fixie road bike yet but will soon, so would like to know my options.

Threaded. If you're going to use splined cogs you need a matching thread-on cog carrier.

Thanks for this. :)

Threaded, whether it's fixed or freewheel. And if it's fixed, a lock ring, which has the opposite thread.

Yo are those any good? Or do people just use them because the Miche cogs end up being a little cheaper?

I have Miche on one side of my wheel -- chose it so I could do quick and easy cog changes at the track. Mission accomplished there. The cogs themselves are fine, can be a little noisy sometimes but I don't mind that too much. I've used them on the road too and they've held up well so far. If you do frequent gear changes, they're good for the convenience. Limited sizes though, and running them without a lockring is never an option.