New to HF and hearing lots of different phonetic words - some guys say 'America' for A or 'Germany' for G. I thought we were supposed to use NATO phonetics (Alpha, Golf) for consistency? When do experienced ops deviate from the standard and why?

Also hearing contest stations switch between different sets - is there some advantage I'm missing?

You're encouraged, but not required, to use the NATO Phonetic Alphabet. Many operators use informal, alternate words (America, Germany, Sugar, etc.) The key is clarity under current conditions - sometimes switching phonetic sets helps when one isn't getting through.

If the other operator is having trouble picking my callsign out of the noise, it sometimes helps to switch phonetic alphabets. Sometimes one or the other sound just happens to get through better or is more recognizable by the other radio operator (especially if English is not their primary language).

A callsign such as WØLPR might be "Whiskey Zero Long Playing Radio." Certainly easy to remember but if you use these phonetics on the air under marginal conditions, you'll probably just confuse the operator on the other end. Stick with standard unless conditions force a change.