Tankless systems are inefficient and best used where space is at a premium.

Indirect systems cost more to install than stand-alone tanks, but may save in operating costs.

I've put in water radiant systems in poured basements and the clients love them. But to get the most efficiency, they should be sized in combination with the central heating system. Personally, I don't mind that the basement floor isn't toasty warm in winter.

Here is a link that might be useful: US Dept. of Energy: Tankless Coil and Indirect Water Heaters

We put in 2 tankless hot water heaters and are pleased with our choice. One serves just the master bath which probably uses hot water at most 20 min a day out of 24 hours and there is no tank losing heat all day long. One thing I don't get though, is the indirect system requires that you fire a boiler to get hot water... so you have to run the boiler all summer long or as we do in winter, we heat the house with wood much of the day so the heater is just off. With the tankless, you only need to heat the hot water as you use it.

Here is a link that might be useful: comparison

I 2nd worthy. Tankless are arguably not cost-effective, trouble prone and introduce combustion gas concerns. If you have a basement, I highly suggest a heat pump water heater.

Radiant floors are another questionable choice. If you are in a climate that needs a heat pump for cooling then radiant floors are a very expensive redundant upgrade. If you can feel the heat from a radiant floor, its a strong indication of a poorly built thermal envelope. Combined with very slow responses to thermostat changes, these issues may wipe out perceived comfort benefits. Take the extra money to upgrade to radiant and put it into air-sealing, insulation and fenestration.