There are more easy golds than there are hard ones, we should just make a list of the ones to avoid.
The following two gold medals were total hell for me to get, I regret getting them and should have waited for something easier:
The Long Stretch (the drug mission with Franklin, Lamar and the other guy). The time constraint is rough.
Mr. Philips (or was it Mr. Richards?) - The one where Trevor needs to kill every fleeing biker. Absolute hell.