Are all emulsifying agents created equal My question relates to the 5 of 6 emulsifying agents I am aware of for stabilizing emulsification. 
namely; egg yolk, garlic, mustard, tomato paste, honey, and cream. 

I haven't personally used each of these as as emulsifying agents but that's the extent of my list. Anyways. So my question is, for any given particular emulsion does there exist a most useful emulsifying agent to Stabilize that particular emulsion? For instance, if I am making an oil in water emulsion, like a hollandaise sauce where the emulsifying agent is the egg yolk or whatever, would egg yolks yield an equally stabilized emulsion if used in an water in oil emulsion like a vinaigrette? Or would an alternative absent be more appropriate for that type of emulsion?

Again, not interested in any specific case, more of the general answer. I imagine the emulsifying agent is useful because it has both a hydrophobic and a hydrophilic side, kind of like dish soap, which lends it to uniting oils and waters so well... I don't know though if there are particular characteristics about specific emulsions that would make mustard more appropriate in one case but not as desirable in another.

Obviously this is assuming all other variables being equal, and with out consideration necessarily of taste... I mean this is cooking so everything has to do with taste but you know what I mean
From a chemistry standpoint, yes, there is a difference. That depends on the desired effect and composition of your emulsion, so there are more appropriate emulsifiers for water-on-oil than oil-on-water, and also depends on what size of micelles you want forming, texture and etc. 

A complete explanation is a whole course in university and depends on a lot more details, so that's the condensed general version.