Fermentis will give you the basic yeasts. Pretty good yeasts, but 'standards'. Wyeast and White Labs produce the same or similar yeasts, and where they are the same, I would recommend using the Fermetis yeast due to cost and ease of use.
What Wyeast and White ;labs have, is a much greater selection of yeasts for different styles, flavors, attenuation, and flocculation. Many of the yeasts have their origins in different breweries. If you can't get them you might want to research beers that have live yeast in, and try culturing the dregs to get hold of some different strains.