I first lived with natural gas (NG) for many years. Then my wife and I moved and lived with a propane condensing furnace for 15 years; there was no natural gas where I lived at the time. The propane furnace was fantastic. We moved yet again, and now back on natural gas. Still great.
Why? Because generally other than the burner orifices and regulator, furnaces (and most other gaseous fuel appliances) are the same. We first were on NG when we got a new gas dryer. Then we moved outside the city and I bought an OEM kit to convert it over to LPG and did it myself. Then, when we moved back into NG supply area, I converted the dryer back again. Furnaces can be done the same way; the orifices are changed out and the pressure regulator is modified (typically by a spring set kit).
Unless otherwise stated, my all appliances are sold as "NG" units. Some companies will sell LPG units at the consumer level (such as blue flame wall heaters, water heaters, clothes dryers). Other appliances are larger and simply converted upon installation (like whole-house furnaces).
My point is that regardless of the fuel supply, if the unit is a good performer, it will do so either way, if set up properly.
Brand loyalty? That's no difference than oils, guns and girlfriends. Some have it; some don't. You decide.