What icing recipe works best for a wedding reception, outside in the Texas heat and humidity? I know there is a professional heavy duty shortening, but I can' remember the name of it.

Depends on what time of the year you want to use it. If it's in the cooler months (this being Texas, I have to add "either one of them"!), the good old all-(trans-fat) shortening buttercream works fine. Fondant with ganache under it is probably better, but you may not want to go that route. If it's for the warmer months, the answer, unfortunately, is "none of the above". I'm originally from Houston and the climate where I live now is comparable to May-June in Houston, but all year round, so I know whereof I speak.