Extensis Suitcase all day long. Been using it for about 8 years now, maybe longer. The advantage? That you've even asked the question means you need it! Personally I've got over 6,000 fonts and without Suitcase the system speed is bogged down having to load those all everytime I boot, again when starting any application that uses fonts. Also a lot better for previewing fonts than anything built into PS etc.