I have always used the US citizen line when traveling with non-US citizens (I am a US citizen). I've only ever done this in the northeast (almost always New York), and I've heard that this is frowned upon in Texas (or at least at Dallas-Fort Worth), but I have been repeatedly told in NY that it's the proper thing to do, so the practice appears to vary by district. But if you're traveling with a US citizen, and you're going to New York, go to the US citizen line.
Your question seems to imply that you will be traveling alone, however. In that case, the answer is pretty easy: as someone who has a B visa, you should not use the visa waiver program. In fact, if you have an ESTA and try to use the VWP, and the immigration officer notices that you have a visa, the immigration officer should admit you in B status. Technically, one condition of using the VWP is not having a B visa. Of course, this doesn't always happen, because immigration officers work quickly and it's easy for them to overlook things like that.
In fact, the line you use does not determine the status of your admission -- all officers should be able to handle all statuses, so as far as the pros and cons of choosing a particular line, that is really a secondary consideration. The main thing you should be aware of is that you want to be admitted in B status (rather than in WT or WB status as a VWP visitor).
Why is that? The most obvious reason is that B visitors are typically given six months' admission, while VWP admission is for 90 days. Furthermore, VWP visitors are generally prohibited from extending their stay or changing their status, a prohibition that does not apply to B visitors. Finally, an applicant for admission under the VWP waives various sorts of legal rights that you hope you will never have to exercise. These rights are not so important for most people that they go out of their way to apply for a B visa, but since you already have a B visa you should ensure that the officer admits you accordingly so you don't have to waive them.
Or maybe I misremembered and there is only one line?
I don't follow it very closely, and the criteria have changed, I think, as the automatic passport kiosks have been brought into use, and I think the criteria even vary from one airport to another. However, I believe that in most airports both VWP travelers and B visitors are eligible to use the kiosks. You probably won't know for sure until you begin approaching the immigration hall and read the signs.