I do neck once a week. I love training the neck. My neck is thick and not lagging at all. With all the other compound movements your neck gets a lot of synergy but adding 1 to 2 sets a week makes a huge difference. I've found for me anyway, the neck grows rather easily. I posted a towel method for training the neck. Its easy and you'll feel it the next day for sure. I would do them cobin as long as you got energy left to do them. Thats why i usually do them first.
Scaggs