We are looking to start using visitor groups on our commerce site after having been live a few months I'm curious for those who have been on Episerver longer, which Visitor Groups have been the best performing in terms of your goals. We're looking to drive more sales from customers and want to leverage the learnings of the community if at all possible.
Instead of showing the same products to every visitor, personalization can help in showing the exact product the visitor is looking for. I think the following link can help you for exactly what you are looking for. Instead of asking to others, you can read here more about the what are custom criteria's Episerver commerce provides, that can increase your conversion rate.
Let me know if you need more help.
Each site has a different set of customers and different buying behaviors, so it's very hard to say which visitor group is better without knowing the site (also it might be seen as a trade secret). You can however try out with A/B testing to determine which approaches are best for your site. Take time to run the tests and analyse the results, yes, but in the end it might be worth it. https://webhelp.episerver.com/latest/en/cms-edit/ab-testing.htm
And Praful's recommendation regarding Personalization is also a good idea.