Need to replace a gas hot water heater with direct venting. Currently have a 15 year old 75 gallon unit. 4 in family (three baths). Never take more than 2 showers at a time or within an hour (unless we have guests). But have growing kids. My plumber uses AO Smith and thus I've been doing my research on their different options. He suggested a 75 gallon replacement. I started to look into more efficient units and identified two: XGV-50 and the vertex (highly efficient) models.

The XGV-50 has 88 gallon first hour delivery but recovery of only 41 gallons. It has 40,000BTU input/hour and Energy factor of .62.

The Vertex model (GPHE-50) has 127 gallon first hour delivery, 92 gallon recovery but uses 76,000BTU input. 90% thermal efficiency.

The 75 gallon unit doesn't have a first hour delivery rating, recovers 81 gallons and uses 75,100BTU (model PCG75 or FCG75). No energy factor rating.

I have no idea how best to make a decision. I want to be conscientious about energy usage but dont want to be in a situation where I'll regret having to take cold showers. Any thoughts on how to decide size/energy effeciency or experience with these (or brands) models?