One thing to consider about tankless units is the incoming water temperature in your region (think, winter, coldest case) versus the temperature rise the unit is capable of.
If you live in a cold climate an have upper 30s F or low 40s F incoming water, and the unit can at maximum heat 60 degrees above incoming temperature, you'll never get the water hot enough to enjoy it. Check the specs for the heater you are looking at... a lot can only do a 35 degree rise at maximum flow rate, or a 60 degree rise at the lowest flow rate... Electric units generally can't raise the temp as much as a gas unit, but it will vary by unit.
When in ~2012 I was looking at a new water heater (replacing one under warranty, interested in upgrading tankless), the plumber here (in Indianapolis) cautioned me that the current crop of heaters wasn't up to the cold water temperature in winter in this region, and that it would struggle to keep a hot shower hot. He felt in the not too distant future they would be able to do enough of a rise to make it worth it. That was 4 years ago, so perhaps things have improved.
When my Bradley White tank unit dies, I will strongly investigate a tankless unit. I've got a gas water heater now, and would go gas tankless.
Marc