Which turntable to keep?

I have both in my TT collection. That's a tough choice to make! 

Good question!  Personally, I have always been partial to a Dual and frankly I think it is a better TT than the Miracord.  On eBay, you can get almost twice as much for the Dual as the Miracord, so clearly a lot of folks think so as well, and there is a message there.

Another option, and a better option besides, is selling both, adding some pennies, and buying a better TT.  Most of the TT's in the $500 to $700 price range are significantly better than either of these vintage units. The Dual is a cool, vintage unit, but if it was my system, I'd sell both and upgrade.

You didn't mention what cartridge you have on them and that is a significant issue as well.  

Upgrade and toss the old ones!