Gregg Williams has a plethora of coaching experience as both a defensive coordinator and head coach.
Freddie Kitchens has his first job running an offense, an offense that is VASTLY improved.
IMO, it is a no brainer to go with Williams and let Kitchens further his experience. I do not see any team going after him based on 1/2 season running an offense. Kitchens has a lot of tools on offense he can work with and establish a pedigree for success. The best thing he could do is interview for the position, continue to build his offense, win this team a division title, and then see what is available.
Let us say he goes to Arizona. They have a rotten offense with a vastly declining Larry Fitzgerald. The tools he will be given are not as sharp as Cleveland and won't have the same successes he has had in Cleveland.