Ok so to prestige you need Bane's Faction and Joker's both at level 30 when this is done your combined total should be 30. go to character load out screen at the main menu and you will see prestige option
So basically I figured out a way to get 40,000-60,000 with Bane faction and 30,000-40,000 with jokers faction separately and together roughly the same with Joker but about 30,000-50,000 with Bane. Batman gets about 1,000 but it counts for nothing
With three people decent xp for both
Setup: I recommend Wonder City map and use the lighting bolt Control Point
Have Batman stand close to Joker faction guy I had him crouched on the rail so he wouldn't move when hit by the crossbow
Step 1: let the Joker faction take the control point
Step 2: Joker faction leave control point
Step 3: Bane faction enter control point for 1 second
Step 4: Joker faction enter control point to recapture it then leave again
Step 5: when you can as Bane faction fire crossbow at batman and Jokers guy
Step 6: repeat
You retake it and can get 125xp every 2-3 seconds if you get into a rhythm that simple.
This can work with any number of people just pair up.
The last time we did this we got 32,000 with Bane and 28,000 with Jokers but with a lot of mistakes and loss of rhythm