For those of you wearing rare items, it must have +one resist of your choice. It can also have all resist if your budget allows it, this is known as double dipping. Some of you have items that have all resist, but are missing +one resist. This is a huge waste because +one resist is a very inexpensive stat. It gets trickier with legendary(including set) items because they can usually only roll 1 or 2 randoms. Your best random is usually going to be +one resist. Avoid +all resist as the random if there's only one random to choose from unless you are very rich and you want more than +60 of the correct resist type!
This makes Inna's set a major problem because only one stat can be random. Usually, you will want that random to be +one resist of the same type as it's the cheapest stat. The helm is the lone exception where one random can be +one resist and the other can be an ehp booster such as all resist, percent life, armor or even life regeneration, health globes or gold pickup. Keep in mind that +one resist can be up to 60 and this boosts ehp similar to 150 vitality, but obviously the resist will be far cheaper! You will have to make up the loss of vitality elsewhere for any item that is missing this very important stat.