Well, first off, in traditional counterpoint thinking, it is actually desirable to sound like a second "lead instrument" because all voices can be thought of as having their own melody going.
Secondly, the answer is: all of them. In counterpoint, each voice is as important as the other and they are all "interlocking".
I highly doubt you want a classical Renaissance type counterpoint in your music, so the answer is: it depends. Maybe you can find middle ground and incorporate melodic elements of both guitar and vocals. However, if you want to employ counterpoint techniques, your bass will stand out. So beware if that's not exactly what you want.