Fire Blast is 140xSTAB
Solar Beam is 180
For Fire Blast to be the best neutral move, STAB needs to be greater than 180/140, so approximately x1.3 for STAB.
But STAB has not changed, or at least none of the smart people here or at the SilphRoad have noticed, so this is a moot point.
PoGoMoves.com ranks E/F highest, but the numbers are incredibly close.
PokeBattler is more accurate and places SW/S higher. (Going against Snorlax Z/HS raid with sun to force Ho-Oh into the ranks of a neutral matchup.)
GamePress is GamePress. I think their Ho-Oh rankings are heavily weighted for Machamp raids, for whatever reason.