As far as operating in the US and associated areas is concerned as long as you accomplish a reversal on the correct side within the alloted distance (unless a specific entry type is depicted, and a 45/180 is not a "specific" entry, it's just a guideline) you can do any sort of entry you like, personally I prefer a teardrop starting over the fix if the hold is on the "far" side from me or a 90/270 if its on the same side.