I usually end up maining a character that us usually a jack of all trades type of character and/or has good footsies + good buttons. My secondaries are characters I like due to playstyle, looks, or just the character himself.
Playstation Allstars:
Main - Evil Cole (Jack of All Trades, Giga *Falcon* Punch was hype, Badass character from Infamous series)
Secondary - Sweet Tooth (Fun to play, fun to troll 2v2 pubs as double sweet tooth, beings out a lot of salt)
Injustice:
Main - Green Lantern (Jack of all trades, B13, Yellow Lantern Costume, Fan of Green Lantern Animated Series)
Secondary - Joker (Favorite DC Villain)
MKX:
Main - War God Kotal Kahn (B1 *kreygasm*, Footsies, He's just dat nigga man!)
Triborg Smoke - Smoke *kreygasm moar*
Secondary -
Ninjutsu Scorpion (Footsies, easier to combat online scrub tactics)
Ronin/Lasher Takeda (Least used variations, footsies are fun, getting a new skin!)
Gunslinger Erron Black (He has a hat!)