Depends on what type of a site you want to develop, your expertese and the type of budget you have.

From personal experience I have found gigabot to be quite buggy, it was a big hog on the resources so I have IP banned it, there are only three bots that really matter though, msn, yahoo and google.

Have you thought about creating dummy accounts and start discussions between them?

Ah yet another member from TAZ comming along, anyways I have the same question which gazaa and csgal asked how do you pay them well that does explain the placement on big-boards.com though.