How cold does your water get in the winter? The things have a couple of deficiencies, in my view (they can be overcome, but it usually costs more): they can only raise the temp of the incoming water a certain amount at any volume (typically about 70-degrees), and, they don't generally turn on until the flow rate is over say 1/2-gallon/min or so. If you like to have warm water at the sink for something, you might need to run both the hot and cold fairly high to get the flow to cause it to turn on. Too low, no hot, turn it a little more, and it may jump in temp radically once the thing actually now senses it needs to be on.
Installation costs are generally a lot higher than a tank. Depending on your water, a tankless may need to be de-limed annually. So, running costs may be lower (but standby losses aren't huge), but maintenance costs are likely to be higher. You may or may not ever break even verses a tank.
How were you planning to power this: gas, propane, electric? I would not consider an electrical tankless except maybe for hand washing only. One large enough to provide decent flow would likely require upgrading the electrical service. Some places base their minimum charge on the capability - bigger possible service, bigger base costs (even if you don't use it). This is in addition to the per KWH use. Unless you have really ecconomical electrical rates, I'd not consider that type. Gas, maybe, electrical, no.