Boots are like underwear. What is comfortable for you may be uncomfortable for someone else.
Personally, my favorite are Courtney safari boots. I've used the same two pairs for years and have found them to be comfortable and rugged. Available from Westley Richards and African Sporting Creations.
Russell PH boots also work well, though fitting can be a pain, as they are made to measure and Russell doesn't always get it right on the first try.
