I prefer to use rubber curries for grooming. There are many different styles of rubber curry combs. I have a wide variety of styles and use the ones that each individual horse seems to like the best. Also, I tend to find that the course finger or larger finger/nubby styles of rubber curry work best on thicker winter coats than other styles and the finer, softer styles and the mitts work best for fine, shorter summer coats and thin skinned sensitive types. Some horses will still prefer to be groomed with the course, larger nubbed styles though, even with a summer coat.
I only use a metal curry for cleaning the dandy and body brushes, I don't use it on my horses.
I've never used a plastic curry, so I don't have any advice on that style.
Whatever style works best for you and your horse is fine!