We do not have a particular recommended printer. Google Cloud Print is designed to be compatible with any printer at all, and it is unfortunately not economic for us to invest in testing different printers, given the pricing expectations of the WooCommerce extensions market.
Any printer at all that you can connect to your computer and print from, and also any stand-alone printer that has Google Cloud Print technology built-in, is suitable for use with this plugin. We are aware of customers successfully using a wide range of makes and models of printers, including different thermal printers.
We first tested and developed the plugin using (among other things) a Star TSP-100 thermal printer in 2013, and are aware of customers happily using this printer still today several years on, but this does not constitute a formal recommendation.