I think most of the show folks use a 48 X 24. It is large enough to stack a dog out on while trimming. Most of the pro groomers use this size, I think.
If you aren't showing and your newf is not the XL size, a 42 X 24 is adequate.
I have a 36 X 24 and it's kind of tight for Gabriel to turn around on...If I were doing it over, I would go with the 42 inch.