Is it better to intern at a new organization or the previous organizations I have interned at before?

I'm a degree student who's had two internships experience before. The first one was in July last year, and the second was in July this year.

I'm entering the final year of studies early next year (just finished my second year) so basically I have two major semester holidays left (the one I'm currently having is until end of Feb while the next would be during next July, for a month). Therefore I would like to make the most of these two major sem break before I enter the working world.

Pros of interning at one of the two previous organizations
- I know the people there and the environment (though I wasn't so comfortable in the 2nd organization. The people in the first organization was lovely though, and I keep in contact with them. I have mentioned to them that I may work with them again)
- I am interested in the issues that these organizations promote (youth rights, women's rights, governance, etc).
- I wasn't in the organizations for long (roughly a month) and by going back there again hopefully I can solidify my work experience with them. I'm also hoping for a solid reference from them.

Pros of interning at a new organization

- Variety, not just in term of the organization itself, but also new people and also new issues (some of the issues include: refugee work, sex workers, transsexuals, gay men, etc. Though I must admit that I'm not interested in these issues as I am with the issues I've worked with before. Still, I'm young and still in the process of finding my interests).

Please advice! Thanks in advance.