If you always plan on staying in RV parks, maybe the tankless makes sense. Unlimited quantity of hot water is the draw, that means you also need an unlimited supply of water, and the means of draining it off, and in those ads they dont mention that they are usually on a supply of only 20 to 45 lbs of propane. Taking those long luxurious showers the ads claim, will have you running constantly to refill propane. And when you run out its not just hot water that you lose, its cooking and sometimes even heat.
The standard units which can operate by both propane and electric give you the ability to take showers and to complete other task, maybe not in "unlimited " fashion, but with a little experience, you will quickly become accustomed to it.