Best macro lens for Canon EOS M10

I don't think there is a simple answer to that question.

There is one EF-M macro lens, a 28mm which has just been released (or will be very shortly).

The EF-M 11-22mm offers close focusing at the 22mm end, but not enough to reach 1:1 I believe.

Outside of the M range you have a choice of pretty much any macro lens going. With an adapter you can use EF lenses and retain electronic communications with them - Canon's latest round of macro lenses are all very good as, indeed, are their earlier FD mount lenses (which you can also use with a suitable adapter - although manual only).

You could also use the highly acclaimed Canon MP-E 65mm although it will be difficult to use outside of a studio setup as the M10 lacks a flash hot shoe, and light becomes more of an issue at magnifications greater than 1:1.

Furthermore there are a tonne of options to provide macro capabilities without using a dedicated macro lens (and for very little cost).  Reverse lens adapters, front mounted adaptors or extension tubes can all be used to achieve higher magnification on your existing lens set.

If you can expand on the type of subjects you intend to shoot and what kind of budget you are working with I might be able to offer some more specific advice. Other than that a ~100mm focal length macro lens is a good start if you can find one within your price range, or have a look at the EF-M 28mm macro lens if size and weight are important factors.