Tankless is an excellent option. Cost-wise, natural gas is highly likely your cost preferred tankless or even-tank type fuel/energy for water heating if your home is already served natural gas from a local distribution company or a municipal gas utility. Do the math conversions for cost of a million btu’s (Mmbtu) natural gas compared to propane (1 Mmbtu = 10.917 gal. propane approx.) and to electric (1 Mmbtu = 293.1 KWh approx.) and you'll see the cost benefit. Understandably there other up front, first year installation cost considerations such a possible natural gas meter &/or supply line upsizing, plumbing, etc but your cost saving analysis should be favorable over the long run of 5-10 years.