What salt has the best iodine contents?

Any iodized salt has enough iodine.  Sea salt has much less iodine than an iodized salt.

Kosher salt does not have iodine so avoid that if you need the nutrient.

Morton iodized salt has plenty of iodine.  They don't put iodine in anything but salt so use as much as tastes good on your food.  Still don't add any to canned food as they put in too much at the factory. 

They say not to but I use iodized salt for all my pickling and canning.  Here we have to can as much as possible because of our long nasty winters.  Salt can be as important as meat up here.  You'd be surprised how fast you can run out of salt and get badly dizzy.