I really much prefer small meetings. I get so much more out of them, see more science outside my comfort zone, and I network more effectively. In a large meeting, I sometimes feel at sea. The science is often great, but I have a really hard time making new contacts outside of the session I speak in. It is nice to be able to rebew conference acquaintances, but I often feel that I am not making the most of the networking opportunities at a large meeting.
I just got back from a really great meeting attended by 50 or so specialists in a well-defined area. Many of the participants know each other from previous iterations of this meeting, which I was attending for the first time. As a naturally less social introvert, I find networking and cold self-introductions really challenging. At this meeting, I spoke on the first day, which broke the ice with many of the participants, and was a great help. If and when I organize a similar type meeting, I will remember this, and try to schedule "newbies" early in the meeting.
Also, I found that I knew a couple of the major players already from attending program reviews back when I was at a National Lab. If you are a student or postdoc on a project that does annual reviews, try to go to them (or at least ask your PI). They are a great opportunity to meet the players in your field)even if the program managers change over). Even better is if your PI will let you give some of the review talk, so people in the field will know who you are. These contacts have been great jumping off points for me, and I am grateful to my postdoc advisor for taking me to a DARPA review and having me give 10 minutes of the review talk.