Camera-mounted mics are good only out to about arm’s-length. A shotgun will work at a longer distance, but it’s really for getting people one-at-a-time, with a live boom operator, when there’s more than one person. if you’re shooting from the back of the room to get someone at a podium, a hard-wired Dynamic Cardioid “stick” is the most bullet-proof way to go. An alternative there is to place a digital personal audio recorder on the podium and just let it roll for the entire event, then synchronize it to your program in post. The recorders are cheap, on the order of fifty bucks to a hundred. But that procedure adds time and work.
You CAN put a different kind of mic on a boom, to get two people talking: you’d be looking for a dynamic or condenser mic with a cardioid or omni pickup pattern. Dynamic mics don’t need power and will be cheaper but less sensitive.
Personally, I own but rarely use a boom; I generally operate lone-wolf mode. I tend to use hard-wired lavaliere mics and a mixer for more, if there are more than 2 people talking. By putting each lav into it’s own channel on the camera, I get much better control of audio in post. The lavs can be open or hidden, and can be placed inside clothes to keep out wind or area noise. Pointing them at your shoes may look weird, but keeps breath sounds and wind noise out of them. If you are dirt-poor, you can find cheap wired lavs at Radio Shack and I guarantee you they will sound better than an on-camera mic. Making the lav wireless jumps the cost a lot, but adds issues regarding possible interference, so while I have wireless lavs, I use the hard-wired as much as possible for dependability.
Another mic in my arsenal is one I use for tabletops or on a coffee table, for 2-3 people, and that’s a boundary mic, often also called a “PZM” mic for one brand that pioneered marketing these. Boundary mics use acoustic wave physics turn all of a flat surface like a table, wall, or ceiling, into the sound-gathering device, and also have good noise rejection. Boundary mics are flat and small and hard to see in a shot, easier to hide than a stick mic. They require phantom power from the camera, though.
Get a free catalog from fullcompass; they do a great job describing all the mics they sell in detail. Write back with any further questions. Good luck!