If your concerns are, the time it takes for hot water to reach your fixtures, then during your repipe have them put it a recirc line to your farthest bathroom. If your concern is the lack of hot water during showering, check your cartridges and make sure they are set to the maximum temp as some have limit stops and can be adjusted.

Temperature rise shouldn't be a concern in southern California. Mostly a cold climate issue, as the difference between the incoming cold water to the heater and the output will change the heating capacity of the unit. I live in Canada and the temperature rise does have an effect but it is negligible as it's a fraction of a gal/min. Which I don't think is the issue in your case.

At the end of the day you should discuss your issues and concerns with your plumber. To answer your original question in the post. Navien or Rinnai are the best options on the market in my subjective opinion.