I have had both.
Rinnai powered by gas - won’t get scalding hot like a tank but it never bothered us. Small and no issues in the 5 years I had it. For a 3,000 sf house with 2 young kids it was fine (9 & 10 1/2). Gas bill went down 50%.
My new house has 2 big Rheem tank heaters powered by gas...