Question

When saying vamos, would you say the v with a b sound or a v sound?

Answer 1

With the other explanation, I'd like to complement with the fact that some people pronounce it like a sound in between the b and the v.

Answer 2

most of us DON'T make a dinstinction between b and v. As mentioned before, you may hear /b/eso or /v/eso. Of course, the right spelling is "Beso". But speakers will say in one way or the other without noticing.
And almost nobody can tell them apart. What I mean is that they don't pay attention to the difference between /b/ and /v/. They will rely entirely on context.
The difference between those two is already lost. Some radio host try to keep it. It is funny to listen to them. I try to make the correct sound. But I have to do an effort to sing a song that goes "pásame la botella. Voy a beber en nombre de ella". If I say that without paying attention... I might get some mixed /v/.
I saw this effect when tried for the first time to explain Spanish pronunciation to some friends.
What I tell them is that... natives won't bother to pronounce /b/ and /v/ as different sounds. But they may mix them very often. And if you are wondering how to pronounce them... you can chose the way you pronounce in English and your message will get through perfectly.