DC (and NYC/CHI) is the no brainer, it really shouldn't even be on the list, IMO, because it's so blatantly over the top bad, and yet limited in scope.
Ohio & Colorado aren't the most friendly states, but they don't deserve to be on the hostile list, especially given Ohio's recent rounds of reforms.
Objectively, it's a close tie between NJ & IL for most gun hostile, with NYstate having honorable mention due to their handgun hostility.
The things that separates NJ & IL from all the other gun hostile states is the practical impossibility of obtaining a carry permit, and the necessity of obtaining a FID/FOID for any sort of gun at all. In all the other states except MD, there's a 50/50 chance of getting a permit depending on where you live, and CT has been de-facto shall issue since the early 70's, predating Florida's reforms.
At the end of the day though, it's IL as the all time grandaddy gun hostile state. The two things worse than NJ is that the FOID expires, whereas the FID is good for life, which potentially exposes gun owners to risk of arrest & etc if they stop renewing their paperwork. The other thing is the lack of state pre-emption, which means that any coffee klatch of noisesome old biddies can get together and ram something through town hall to deprive you of your civil and human rights.