The Justice league has faced many enemies over there many incarnations but none as persistent as Darkseid. Darkseid is one of the most powerful New Gods and the ruler of the planet Apokolips. His entire life has been spent gathering power and subjugating various life. All of this to find the Anti-Life equation, an equation that upon being heard by anyone would make them lose their free will and serve Darkseid.
Darkseid has recently been the object of a lot of speculation as to whether he will be in the first Justice League movie, or in later films. Below are some Pros and cons, yes I realise there are contradictions in my list.
Pro's of using Justice League
-Most Darkseid stories involve Darkseid trying to take over the earth, it would be a simple reason for the Justice League to form and would not require a lot of background info when you already have to introduce the Justice League members themselves
-Probably the most popular of the Justice League bad guys, could drum up some major hype.
-Parademons would make excellent canon fodder for the Justice League members to display their individual powers on.
-Opens up the DC New Gods mythology, could lead into characters like Orion/Big Barda/Mr. Miracle
-Darkseid is a villain who could come back in later times like he usually does in comics, if he does appear in Justice League, I wouldn't be surprised if it ends with Darkseid retreat back to Apokolips.
-If he was a good villain people will want to see him again
-Yes we saw Thanos on screen first, but we could see Darkseid raising hell on Earth before Thanos does in Avengers 3 if that 2017 date is real. If DC and Marvel's biggest villains are both alien warlords intent on controlling the universe why not get yours out first.
Cons of using Darkseid in Justice League
-Darkseid could be used as the endgame villain for a Justice League 3/4 much like Thanos.
-He's to hard to explain for the for the first Justice League movie
-Plot of Avengers 1, Avengers 2, and Justice League 1 would be a maniacal bad guy with an endless army of expendable soldiers.
-Unlike the MCU the DCCU has a goldmine of unused characters at the moment, they could use just about anyone as there first.
-Darkseid should be the final villain, like Thanos he should be teased throughout many movies.
-Darkseid's place is in a Superman movie
Anyways in my opinion, with the DCCU being set up the way it is there first villain shouldn't matter too much. It's introducing the team and team dynamic that matters the most. I'd be fine with if they made Darkseid the big bad for the first Justice League as long as his origin doesn't take too much away from the heroes.
But then again if I had my way Darkseid wouldn't be the final endgame villain for the Justice League, thats reserved for this guy.