Tankless water heaters?

I don't have one but have been checking into replacing my 15 year old electric 40 gallon with a gas tankless

What I have found. The smaller one I have been looking at needs Stainless steel flue (EXSPENSIVE) and the larger uses PVC. So I'm thinking the extra cost to get the bigger more costly will be offset by the installation cost.

A guy I work with has his own HVAC company and he has installed a lot and said I needed larger gas line (one reason I'm still just looking and checking into it) have not seen anyone recommend a whole house electric unit.

Since I may be moving in the next year or so might just put another electric 40 in and be done with it.