If you are in the US or Canada, you may or may not want to upgrade to Money Plus. There are some advantages including multiple version backups. However it does depend on Internet Explorer, so there could come a time when Money 2004 would have some
advantage.
If I were using Money 2004 elsewhere, I don't think there would be an advantage. Don't lose your Money 2004 install disk.
But to answer your question, the answer would be Money Plus if your Money file is from North America, and Money 2005 otherwise. See what is currently the second post in this forum.