As someone whos job was to oranize visas for various countries around the world for some time, here is my advice. If you are doing this kind of semi-business/semi-pleasure/speak-at-aconference/whatever trips, just get a tourist visa. Everything else is a giant mess.
If you go to a conference in the US (merely for attending) you're entering for business purposes. If you have only a B-2 visa, you will be turned back