There are six different Monarchs of Great Britain who have ruled since stamps were issued. Five of them have left a very prominent philatelic footprint (Edward VIII was king for a bit less than a year and made no impact on stamp collecting). Certainly Elizabeth has had the largest number of stamps issued with her likeness on them, followed by her great grandmother Victoria, but it is in specializing on the three kings in between that has produced some of the most interesting areas to collect. Of these three kings, many philatelists consider George VI the most interesting to collect.
The stamps of George VI are the most affordable of all of British Commonwealth. They lack the rarities of Victoria, the long sets with expensive Pound values of Edward VII and George V, and the tens of thousand of stamps that a complete collection of QE II would require you to own and house. There is compactness and affordibility with George VI. What many specialists consider to be this specialty's greatest aspect is the many perforation varieties and shades.
Over the last twenty years British collectors have largely had to specialize within theframework of Commonwealth collecting. This has been caused by the huge increase of QE II issues, which 
makes collecting this area very expensive and time consuming to even keep up with. let alone expand to earlier periods. And the popularity of British stamps world wide, and especially among Eastern European collectors and the former Soviet Union, has pushed up prices of the stamps of the earlier reigns to where collecting the entire Commonwealth is more of a nightmare than a dream. A George VI philatelic specialty gives a collector all the joys of British Empire collecting with manageable and affordable limits.