As a general catalogue Krause is the standard. If, however, you are specializing in a particular country, you should get a specific catalogue for that country.... for example I would not want to rely on Krause to manage my Canadian collection... there is not enough detail at all regarding changeovers, inserts, plate number varieties etc. I imagine that collectors of Australian note, for example, would feel the same way about Krause. There are countries in Krause that do indeed receive very detailed review - the BCEO countries (West African States) are an example, and if you need info on notes from Sri Lanka, Mauritania and Falkland Islands (for example) - this may be your best resource.
Krause actually comes in three volumes. Vol I is the specialized issues, Vol II is General issues up to 1961, and volume III is 1961 to date. Volume III is updated annually I believe, and I just bought the 13th edition at the show this past weekend.