EA was founded in May 27, 1982, San Mateo, CA
Activision was founded in October 1, 1979, Sunnyvale, CA
I don't keep up with modern gaming so I don't know, but both these companies are really big fishes, which one do stick up for, Activision is somewhat responsible for the Call Of Duty Series and tons of older great games I've enjoyed in childhood including Heavy Gear, and the Mechwarrior series 1 and 2 for the PC, and some of the greatest video games for the Atari 2600 era were also done by Activision.
EA what what I hear are responsible for Star Wars Battlefront and Battlefield and Medal Of Honer games. I personally was disappointed in what EA did to the sims series, after the sims 3 PC series came out. it seemed like EA was starting to get greedy in and around the year 2009
If I had to choose I'd Choose Activision, I enjoyed the Call Of Duty Series, and some of the Atari 2600 ROM's on the "Activision Anthology on PS2" are great for being early 1980's games.
Although I love EA Sports Retro games like PS1 era and PS2 era and SEGA Genesis era though