To be an attractive specialty, a country should have many different things. The stamp issues should be well designed and have a strict postal purpose and not be designed for collectors. The Goldilocks’ theory should be in play: there should not be too many stamps issued, and there should not be too few stamps issued—rather, it should be just right. The stamps have to lend themselves to specialization by issue, and there have to be detailed catalogs to let collectors know what is available and what is needed. And the stamps have to be affordable.
Probably the country that meets all of these criteria best is Denmark. There is only one stamp that sells for more than a thousand dollars and few that are more than a hundred. The whole country can be had for well under $5,000, which for a collecting specialty that could last a lifetime is pretty reasonable. And each of the classic issues lends itself to intense specialty on its own should you so desire. You can collect cancellations (and the Danes kindly used numerals in rings as cancellations on their early stamps, with each number referencing the town from which the canceller was used—#1 for Copenhagen, and so on) to make cancellation collecting easy and fun. On the late nineteenth century Post Horn issues, there are watermark and frame and color and plate varieties galore, and almost none of them are very expensive, even if they are hard to find. And the twentieth century (and later) stamps are among the most beautifully designed and executed engravings that the hobby has to offer. If this wasn’t enough, Denmark never joined the Euro and isn’t in the habit of demonetizing their mint newer issues, so collectors who collect modern Danish stamps always have a postage basis for their stamps, so they have retained much of their value.
So if you are considering a new philatelic specialty, take a careful look at the stamps of Denmark.