According to ConsumerReports.org, the top brands of gas heaters as of 2015 are American Standard, Bryant, Carrier, Lennox, Rheem and Trane, with no statistically significant differences in quality among them. The brands can be compared on their website, where many criteria by which to judge gas heaters are included.
Factors by which to judge gas heaters include air filtration, variable heat output and ignition system. These factors contribute to the overall quality of the heater, including how much noise it makes, how dependably it operates and how often it requires repairs. Each of the brands listed above are compared based on these criteria on ConsumerReports.org.