Virginia Tech is widely regarded as the best third-party, independent testers of helmet impact severity at the high school and youth levels. Virginia Tech ranks helmets on a 1-5 star rating system. On their scoring system, the lower the score, the better the score. (i.e., a helmet rating of 1.35 (Schutt F7 2.0) is better than a helmet rating of 4.49 (Riddell SpeedFlex)).
The NFL and NFLPA also release a ranking chart, but that is only applicable to impacts/hits seen at the NFL level.
"Since 2011, Virginia Tech researchers have been providing unbiased helmet ratings that allow consumers to make informed decisions when purchasing helmets. The helmet ratings are the culmination of over 15 years of research on head impacts in sports and identify which helmets best reduce concussion risk. This work is done as part of Virginia Tech’s service mission and is 100% independent of any funding or influence from helmet manufacturers."