Berkley Vanish is a good choice for a mono for vertical jigging because it is fluorocarbon. One of the attributes of fluorocarbon is that it is low stretch.
That said, when I vertical jig, I use Berkley FireLine. You will find that because of the no-stretch attribute of FireLine, it will be very easy to not only feel bites – but maybe more importantly – you will be able to feel the bottom and maintain bottom contact much better.
Over the past couple years I have been vertical jigging with Crystal FireLine. This stuff is translucent in water and in many situations I have found that I get more bites using Crystal than Smoke or Flame Green.
I use 6 lb FireLine when vertical jigging – the 2 pound diameter also helps cut through the water to keep your presentation as vertical as possible. But it is strong enough to pull in any walleye (I caught my biggest walleye ever on 6 lb FireLine – it was 15.8 pounds).