I've done free base nic, salt nic, and nic polacrilex. Salt nic would be, in my opinion, the most habit-forming (but not addictive), due to a quick and high "peak," and quicker clearance -- leading to a need to re-dose more often. That's also granted that the route of administration (vaping) allows for an insane amount of nicotine to be absorbed, much more than you can ever get with pouches, gums, and patches.

As well, I'm not certain, but I believe Zyn uses salt nic, and not free base.

I've done snuff as well, and it's similar to nicotine gum (except being more of a nuisance).

I haven't seen evidence for basic nicotine products being addictive. I have little comprehension how something so mild can become addictive. Habit-forming? Yes. Full-blown addiction? No.

Cigarettes are different. They're a cocktail of various psychoactive chemicals that get dumped straight into the bloodstream in large amounts. I understand how they can become addictive. I have first-hand experience of all the necessary things that must come together for the "addiction" switch to come on.

In my experience, nicotine alone is not enough for that switch to be flipped.