Question for you master boilers - boil crawfish or crabs first?

Captain Sid's is good stuff.
Use half of the first boil bag and all the seasoning vegetables to boil those vegetables that take longer, such as potatoes. Pull the potatoes and add the well-rinsed (fresh water only) crawfish and the rest of the seasoning bag. Cook crawfish as you normally would. (for what it's worth, I add the vegetables that don't take much time to cook such as mushrooms, corn and asparagus to the pot during the soak when the fire is off. 20-25 minutes in hot water is enough to cook them.)
Remove the crawfish and add the half bag of Capt Sid's boil. Use this to boil your crabs in.
Btw, unlike crawfish, you can purge crabs in salted water. This is recommended so that the crabs "throw up" .