Maples have much better security features (very fine radial lines that you need a magnifier to see near the center). But, Eagles are easier to sell quickly and fetch a higher premium (but you pay a higher premium when buying). There are probably some legal differences in how they're handled regarding reporting of purchases, moving across borders, etc. I've read that Asian markets tend to want pure gold, not 90%. 90% is good for circulation because it's harder than pure gold. Eagles might fare better if they're ever used in a post-USD world for payment. Bars vs coins: coins are far easier for anyone to test for authenticity (ping test) and harder to counterfeit (thinner, round, almost always have a far more detailed design). Bars often also come in sealed assay casing that people don't want to open and believe it must be real because the package says it's real (packaging is easy to counterfeit). If you're buying from a dealer you can trust them but when you go to sell the buyer won't have that same assurance since you're an individual. They do have a lower premium, sometimes little above spot price. Some people stack bars. Weight: 1 oz is by far the standard size. Easier to sell when you need to. Some fractional might be useful if you ever need to sell a smaller amount. Silver is also good to have for this purpose. Coins, bars, other shapes: the more you standardize, the easier you can spot fakes. If you choose popular coins they'll be easier to sell.