I am almost ready to put my summer wheels and tires on, but the tires needs to be replaced.
I would like to have TPMS with my summer set. Tire Rack sells an aftermarket brand, Schrader, which they claim is compatable to our TPMS system for $56 each.
On eBay used OEM sensors sell between $35 to $60 each and new OEM from $80 to $160 each.

I would like to know which is the best choice.

The Schrader's from Tire Rack work fine, just like OEM. I've had a set for two years.

I have a winter set of wheels and tires from Tire Rack with their sensors and as Ron Jr said they work fine.

My only initial hiccup was I would get a "low pressure" reading as I set all 4 tires to the same pressure as they are the same size unlike my 18" OEM staggered wheels. Once I increased the rear wheels to the OEM pressure all was fine. Just an FYI in case you vary your tires from stock and run a different pressure.

I have some from discount tire direct on my winter set. No issues once I dialed in the correct pressure for 20 degrees F. I was told that the units from tirerack are the same thing used by MB.

That's correct. Schrader. Which is what my 2008 came with.