Grabbed this from vg247. It essentially ranks each character in order of the 4 stats. The 4 stats are:
Strength (STR), which governs the power of a character’s normal attacks.
Ability (ABL), which dtermines how powerful special attacks are.
Defense (DEF), which helps to decide how much chip damage you take when blocking
Health/Hit Points (HP), which decides exactly how much punishment you can take before being KOed
Injustice 2: Highest Strength Characters
Each character’s strength (STR) stat determines how much damage they do at a basic level with normal attacks. Gear can enhance or boost these stats, but the base stats represent a starting point and the stats for gear-free tournament play.
Injustice 2: Highest Ability Characters
The ability (ABL) stat in Injustice 2 is used to figure out how much damage special attacks do with any given character. As with other stats, gear can adjust these figures, but the base stats are used in tournament play and are the starting point.
Injustice 2: highest defense characters
The defense (DEF) stat helps to determine how much damage you take while blocking. These stats are the base and tournament levels, and can of course be boosted by gear.
Injustice 2: highest health characters
Health is pretty self-explanatory, really – the more health/hit points (HP) you have, the more hits you’ll be able to endure from enemies before being knocked out and losing a round. Gear can raise this stat as with any other, but below are the tournament and starting levels.