Canada The Royal Canadian Mint for investment grade bullion. High security and standard designs. Excellent for full ounce gold and full ounce silver. Australia I have also grown to like the Perth mint for its variety: Lots of WWII stuff and lots of animals. Two of my favorites. Gold WWII stuff in 1/10 oz size and the animal stuff (Kookaburras, Kangaroos, Koalas, Spiders, Crocodiles) in 1 ounce silver size. Perfect. UK I tried to like the Royal Mint. But even though the Queen's Beasts designs are excellent, I have no desire to get 2 ounce silver bullion pieces or 1/4 ounce gold pieces. And for collecting, I can't afford full gold ounce size. So that means I'm skipping the series. I would have gladly purchased 1/10 gold pieces and 1 ounce silver pieces. US US Mint: Sorry, I just don't care for the Eagles or Buffaloes. I do love the gold Mercury and the gold JFK, but these enter a little bit more into numismatic territory with their premiums. Austrian: boring China: they use grams not ounces. No thanks. South Africa: Ok, but pretty boring. Love the Krugerrand design, but once you have a gold and silver what else is there to buy? Everybody else: they don't mint their own products, they use private mints, so they don't count for me. What do you like?
Personally, I own a quantity of privately minted silver, and a bit of APMEX gold. As long as it's bullion, it doesn't really matter to me. A good quantity of what I have was minted in the 80s, when silver was at a peak, so, some of the companies that minted silver might not even exist anymore. As for Krugers- they are boring, but they are well known, and trusted in the gold bullion market.
To clarify: I don't think Krugerrands are boring. I think they are beautiful. I think the South African mint is boring because their only interesting product is the Krugerrand and they don't produce much else in terms of bullion.
USA and Canada primarily due to my connections to both, but I think US gold carries notable prestige and acceptance anywhere. Canada in recent years for its counterfeiting protections.