V3.0 is an enhanced version that Mautic released recently I must say. Mautic 2.XX.XX is super stable as far as I have used. Upgrading also requires you to make changes to the custom themes that you use.
So, Unless you know what you are doing, I would suggest sticking to an existing 2.XX.XX version until 3.X.X becomes enough old and the community has tried everything possible with it. I hope, this helps. But, this is entirely a personal view. You can come up with yours and I am more than happy to try things out.
