I personally do not like large groups too much.
There are both pro's and cons in having large roleplays.
I used to be in 1-2 rather large roleplays..
One pro is the fact that you always have someone to roleplay or talk to.
A con is that it gets too crowded. Both with players and posts in local or other chats.
One way we solved this was to roleplay with 3-5 people, in different parts of the map, in local/general (private map) and party chat.
But people are rarely online at the same time all at once. c:
I tend to like groups that are in between. I don't like too small where there aren't too many people to role-play with, but I also don't like too big to where it is overwhelming.
For me, it really depends on the group itself.
As Owly stated, I'm on the fence as well.
Large groups can be TONS of fun with roleplaying and making friends in general. However, large groups can have issues. More often than not, from what I've seen, someone will work hard creating an enormous group for a roleplay, only to have the majority of its members never return again after day one.
Inactivity can be a major issue for any group.
That being said, I think larger groups do tend to be more successful than small ones.
Again, this does depend on the group itself and its members. If the group has an interesting roleplay plot and lots of members to interact with, the likelihood of it sticking around as an active thing are higher.
Smaller groups can be fun, though inactivity again is a downfall more so here, because there are less people, so if one person never signs back on to that character, the whole group suffers because of its teeny size. Still, having a less crowded environment does create a more peaceful, tame atmosphere, where there can be more structure and order to posting without posting on top of each other.
I think either way you go about it, it depends on the group and the individuals in it.