When you're at a table, a boundry effect microphone is a nice way to go -- provided you don't have anyone thumping for emphasis.
I like my Crown PZM-30D. I often use it at Church. In that case, I'm doing live sound reinforcement, while at the same time, I've got a second mix for remote rooms and recording to mp3 and DVD. I keep a PZM-30D stuck to the inside of the lid on the open grand piano. I only run the PZM into the record mix. So, the piano goes onto the mix at normal levels, and, if there is some Q&A or someone stands to speak and I can't get a wireless handheld to them in time, I just crank up the PZM and it picks them up fine with just a little bit of reverb off of the tall walls.
To answer your sub-question: Recording studios use large diaphragm cardioid mics. You can see them in use if you watch the DVD extras on any animated movie. The actors are about four inches from the mic. Not eating the mic, but still very much in your face. The gain is cranked way up, but they're in a dead room. If they have more than one actor in the studio, they're separated by five or six feet to avoid crosstalk. Their goal is high fidelity.
Important factors to consider:
How unobtrusive do you want to be? A big mic and stand in front of each person will get in their way. They'll want to make eye contact with the other participants.
How much will they move around? If they don't talk into the mounted mic, then you're going to have parts of the conversation fade out unless you are there making moment by moment adjustments to the gains. And, your mixer had better have auto-ducking to keep the background noise from all the open mics from drowning out the person talking.
How big is your table and recording space? Individual mics, unless they are lapel-worn, are going to take up a lot of room, and you're going to be pushing everyone further away from each other to avoid cross-talk interference. (Auto-ducking would also help avoid the interference.)
How often are you doing this? Setting up and packing up more mics takes more time. You have more points of failure to check -- cables, connections, knobs, switches.
On the other hand, you can have an intimate conversation around a round or roughly square table with a single hemispherical BZM in the middle. Setup time is short. The BZM actually rejects noise transmitted by the surface it is on very well. If your participants are equidistant, gain issues are nonexistent.
A single BZM mic handled a 9-person teleconference table on a system I helped to engineer 30 years ago. There were millions of dollars of PTZ cameras, switches, projectors, touchscreens, codecs, and satellite uplinks -- and then there was one BZM sitting on the table. All that video and computer gear would be useless if you couldn't hear the other end, but the BZM did the job.