I've had an 'Off Grid' place for a good few years now, being there 3 days a week, four back at home (still have to work unfortunately). Its only a small place with one bathroom with shower and bath and sink, small kitchen, small laundry. So a total of 4 hot taps. I had the same dilemma when installing hot water. After much consideration i ended up going with an propane (LPG) on demand unit. I used a Bosch Hydro Power 16 for several reasons.
Pros: Reasonably cheap to purchase(compared to other models/brands), easy to install and maintain, quite efficient on gas(over tank and pilot based system), requires no extrnal elecricity to run. Instant* hot water (after about 20 seconds of cold)
Cons: Takes some getting used to in operation, one part is prone to failure and expensive to replace, as the units are not manufactured and used to the same degree as the normal grid connected units, parts are harder to come by.
Efficiency wise its one of the things that uses the least gas, probably becase it only gets used 2 to 3 times a day for short showers, washing dishes etc. The gas fridge uses more.
I dont have to heat a tank full time when im not there or wait for it to heat up once I get there if I turn it off.
The part that fails quite often is the is the small water turbine that creates a spark to ignite it once water starts flowing. It is well documented. I purchased mine 2nd hand and it failed after 2 years. The parts are available but hard to find and from memory cost around $250 au. But there is a work around, that although not perfect worked for me. Simply replaced the power source with a couple of D cell batteries with a switch to inside. Switch on hot water. Batteries last about six months.
Requires a certain flow rate to ignite, so hot water has to be turned on first and cold added to reach the required temperature. A bit fiddly sometimes when you want a shower.
Im sure there are better more reliable units available but I was doing this on the cheap.
Its all pressurized to 30psi and uses a small on demand 12v pump, Flojet or similar.
I thought of solar hot water in its various forms, hot water solar panels and tank on roof, gas assited solar, the old layers of black tubing on the roof. It either got needlessly complex or too expensive.
There are many other options off gridders use as well that aren't solar related.
Just my experience for my circumstances.