This year, I lived in Kearney (Tercero South) in a triple. I don't think there were any triples in Segundo North this year, just in Laben and Kearney. If you request a triple, you will most likely be placed in Tercero South, unless they do some changes to the housing assignments the coming year.
Living in a triple is fine; I ran into no problems with both of my roommates. Just be sure to set out some rules/guidelines, maintain good communication if any issues ever arise, and have fun!

I found no problem with the space (it's approximately 20ft by 10ft)--it's a lot more roomier than other triples I've seen at other UC schools, such as Berkeley.