I went through Recruitment just last fall, and last summer, I was on greekchat all the time asking questions. One of my biggest questions was "I'm shy-does that hurt my chances?" Of course, looking back I see that it wasn't a big thing at all. When you go in all of the rooms (or houses, depending on how your Recruitment is set up), all the girls make you feel so welcome. Even if you are shy, you'll find yourself opening up quickly. They ask tons of questions about you and things that you have done. Even though I was very very nervous and wasn't talking to pretty much anybody, before I got in the room, after I walked in the first room I opened up.
Now I have been in my sorority for almost a year. I am not nearly as shy as I used to be. I can actually start conversations with people now
As for formal recruitment vs. a informal (cob) type of recruitment, I would have to say that I would definantly recommend Formal Recruitment. Yes, formal recruitment is very stressful, but you see all of the sororities. A lot of times, not every sorority at a school will participate in informal recruitment. Only one sorority out of four at my school can participate in informal recruitments. A lot of times the only sororities that can participate are those sororities that are under total(the number set by the school's Panhellenic). So, during Formal Recruitment you have a chance at all of the sororities as opposed to just a few.
Hope this helps some. Just have fun!!