Collectively, probably the 2nd. They were bringing anywhere between 180-250 at one point, filling multiple servers with 3 divisions. Although thats just lots of small regiments bunched into one.
Honestly I wouldn't count Diplex because yes he did once or twice bring a full team but they never did more than like 1 or 2 weeks with 79th which was when they got the most I believe.
Plenty of regiments have hit the big 100 attendance mark, including the 18e. I will try go and take a look for some screenshots although my Gyazo doesnt go back for enough :/