Second only to the question of what salt do I prefer when cooking is the question "What is Kosher salt?"
It's not what you think - it actually got its name from the use of this type of salt to put a rub on meats to draw out the blood and make them Kosher - as in koshering meat. But the reason many chefs like to cook with it is that it dissolves easily and doesn't contain any additives. Some chefs even say it has a "softer" taste that table salt - that's probably because most table salt has iodine added which gives it a funky taste. I don't ever buy table salt with iodine added anymore. (If you're worried about iodine in your diet, eat more fish, shellfish, lean meats, dairy or take a supplement. Disclaimer: not medical advice, just my two cents worth!)
I use Kosher salt for a lot of cooking - everything except finishing dishes where I use sea salt. Kosher salt is a lot cheaper than a fine sea salt also which makes it the choice for things like salting pasta water. I keep a large salt cellar next to the stove filled with Kosher salt and smaller salt cellar boxes of my sea salts in the pantry.
What's your favorite kind of salt? Let me know by commenting on this post!