I use Scott for WW. For the countries I collect in-depth, I use the countries' specialized catalogs for detailed information: US-Scott Specialized, Canada-Unitrade, Brazil-RHM, Ireland-MacDonnel/Whyte and Hibernian and for Germany-Deutschland-Spezial.
From an organizational standpoint, I prefer the Michel system. Basically it is organized by design type with all the variations listed as minor numbers/letters all in one place. IMHO, it beats the schizophrenic organization of Scott. I even bought a Michel USA-Spezial for reference. From a practical standpoint though, Scott numbers rule in North America if you want to buy or sell.
Dan
