As a general catalog of all countries, it's the only one (two, there are two volumes actually, General Issues 1368-1960 and Modern Issues 1960-current) to get. If you were to specialize in a particular country, there will of course be better catalogs for that particular country, but at this point it sounds like SCWPM is your best answer. Dave
Since you are still window shopping, I recommend finding an older copy of the catalog to peruse. That will save you some money. You may be able to find one at the library. You may also want to check a local bookstore for a new copy and spend some time looking at it there before buying.
I bought my first book through Amazon.com and got an older copy. It saved me money and then I could decide if the hobby was for me. Haven't regretted it and have since given that copy away to someone else who was starting out.