Our domestic hot water is heated off our our gas fired boiler that also heats the house through in floor radiant heat. Is this the most efficient way to heat domestic hot water? If not would I be better off putting in a standalone gas hot water heater or even a tankless hot water heater?

A standard domestic gas water heater is about 60% efficient. There are many models that do better than this but they cost some$$$.

How efficient is your boiler you have now? That will answer the question.