There is not one brand that is vastly superior to another. Most brands offer multiple types. A modified thinset will work for you but don't purchase the cheapest offering. Usually there's a mid-priced version which will be better than the cheapest one. I choose to use Mapei products. In their case, they offer Ultraflex I & Ultraflex II (and even a III). I'd recommend Ultraflex II. I know you've mention Home Depot before...they carry Custom Products. I'd suggest FlexBond over VersaBond.