Good armor against poison, freeze and fire?

Currently right now I have the Vog Cub set, the Skolver set, and the Dread Skelly set as armors, all of which have resistance against the mentioned statuses.
However, after being told that these sets are not very good at all and that I should flat out sell them, what do you recommend?

Although me being biased about offensive sets (black kat, chaos), those sets are perfectly good if you are aiming for defence.
In the long run you could replace the skelly with the snarby set if you go on a shadow lair sometime, though. Nearly same stats: shadow/normal def, snarby gives vh sword dmg and has only 6-6 points of freeze/poison res, compared to the dread skelly's 8.

I agree that you should probably just keep them. Sometimes a special situation comes along where you wish for a particular armor. One example is Skolver for Ice Queen.
When the next Kataclysm comes around, get the 3-star Black Kat helmet. It's easy to get, and can help you decide whether you want more Black Kat. Consider also Seerus and Chaos.
So you might end up with Vog Cub and Seerus for fire, Skolver and Black Kat for freeze, and Dread Skelly if you really want poison armor.

These are very solid armors. Keep them and continue to build your arsenal.
Never vendor any high level equipment unless you're converting tokens into money. I've regretted EVERY SINGLE piece of equipment that I sold to vendors. I have no idea who you were talking to, but they were wrong. Just... wrong. I know everyone is entitled to their opinion, but their opinion is wrong. Fire is vital for Vanaduke and Firestorm Citadel. Freeze is absolutely horrifying if you are solo. Poison is probably the most annoying status as it cripples your offensive capabilities.