Cabbage is much better tasting and is much healthier when it is fresh instead of frozen.
So if you want the best tasting and healthiest cabbage it's best to eat the cabbage fresh before it's frozen.
Fresh cabbage is better than frozen cabbage because the fresh cabbage retains more phytochemicals and antioxidants which can help prevent certain health issues including cancer.
However frozen cabbage is still healthy for you and cabbage does freeze pretty good and still is okay to eat in things such as salads or anything else.
I sometimes buy extra cabbage when they are having a sale at the grocery store here and I will freeze some cabbage later to use in salads.
The cabbage is still okay but not as tasty as it is when fresh.