I’m not sure what you’re looking for. There is a page at http://www.waterheaterrescue.com on Tankless in the Basics section. As to tank heaters, on my Resources page, for which there is a link at the bottom of every page, there are links to sizing programs that will help you decide how big a tank to get.
Comparing tankless to tank is tricky; tankless makers love to draw unequal comparisons that make their products look good. But tankless cost several times more than tank, are finicky, need a lot of service, and may break before you ever break even on the extra cost.
The common language for comparing tank heaters with each other is gallons, Btu input, EF factor and first-hour recovery.