The optional stats that you get from each of the gear is psudo random. Below is the type of stats that you can get from the optional stats (blue stats) for your future fight gears.
This simple guide will give you some guidelines on how to stack your heroes optional gear stats in Marvel: Future Fight.
Physical Attack by lv. X%
Energy Attack by lv. X%
Physical Attack ↑ +X
Energy Attack ↑ +X
All Attack ↑ +X
You generally should pick the optional stats that match with the heroes’ attack. If your not sure, just go for All Attack.
In general, combat and speed heroes generally use physical attack. Most of the blasters and universal heroes use energy. However, to be sure, check their individual attack and skills to get a better idea.
Physical Defense by lv. X%
Energy Defense by lv. X%
Physical Defense ↑ +X
Energy Defense ↑ +X
All Defense ↑ +X
Go for All Defense as it can cover both Physical and Energy type damage.
HP by Lv X%
Movement Speed↑ +X
Recovery Rate↑ +X
If you are a dodge type hero or stacking dodge stats from Special gears, go for dodge stats.
If you are Groot, consider going for Recovery Rate.
For everyone else, stack HP. It should be noted that first option gear slot should be HP by level, every other at higher upgrades should be straight out HP+.
Movement speed is useless.
Critical Rate↑ +X
Critical Damage↑ +X
Attack Speed↑ +X
Skill Cooldown↑ +X
Defense Penetration↑ +X
If you are running Critical Rate special gear, consider going for Critical damage.
If you are running skill cooldown builds with Skill Cooldown leaders like Iron Man / Sharon Carter or even Rocket Raccoon, go for Skill Cooldown.
If you are running simple damage or raw stats build, you will get the most benefit out of Defense Penetration.
Attack Speed is worthless, and going for Critical Rate is less beneficial without the proper Critical damage.