I used to live and work in Addison and have experience with Monarch. When I first decided to become a CFI, I first went to Monarch. I was having a difficult time trying to complete my CFI and work also. I could never schedule the time off. Then I found out about ATP and came to JAX for two weeks and completed my MEI, MEII, and CFI-SE add on.
I now work for ATP and enjoy it very much. This is a great place to be. That being said, I'm not gonna bash Monarch. I flew with some great guys there.
What it comes down to, find a place to fly that fits your needs. Would I fly at Monarch again, you betcha. Am I happy with ATP, heck yah! Hope this helps some.