Frozen is easier, since its just ordering and stocking. Meat, you have to know cuts, % Fat, now to cook, APP and suggest items to customers. If your interesting in making $$$ Meat is better, but its a lot to know and takes time. Frozen you most likely working by yourself, freezing in your fortress of solitude (Walk in Frozen Freezer) or your finger tips are getting frozen from touching all the items.
Well, if you don't want to deal with as many customers, then frozen is the better choice since all the Kroger stores I've worked at schedule employees in frozen foods overnight. Plus, you should get an overnight premium if it's in your union contract. Since you'll be working overnight though, you'll have to get used to sleeping during the day. Of course, that also means it will be harder to do stuff during the day since that's basically the only time you'll have for some shut eye.