Whatever brand you get, multicoated filters really do reduce flare and ghosting in high contrast situations. B+W and Heliopan have nicer rings, and if you use their ND filters, you may find them more neutral than other brands, and their UV filters are more effective than most others at reducing UV (there was a good article on UV filters, by Bob Atkins I think, on photo.net). Tiffen filters are usually glass-gel sandwiches, while B+W and Heliopan are dyed in the mass, but as Eric says, Tiffen filters are widely used in the movie industry (but they also have budgets to replace filters as needed, pay assistants to clean them, shade lenses properly, etc.).