engineers are strong early if you manage to get pyramid/garden combo in a city you can use the 1st to rush the GL ie, but if so, and as your gold prod capacity grows they become more and more useless, finishing merged in spacepart building cities and wiped into a golden age. Since they don't fall under castesystem availablity they are hard to get when they would be usefull so do not overestimate them.
GS imho are more usefull early on for academies and tech rush (they pull out more beaker than over GP in tech discovery)
Merchants btw are very usefull to merge in late game in your globe city because of the +1 food, early on they are merely useless.
Prophet are pointless if you have no shrines to build or no holy city (without shrine) in target to conquer, i think they are the most useless.
Artist on the other way are very strong, for cultural vic they are simply mandatory to level the culture of your 3 cities. In late game, they can be used as a military unit, capture a city, raze any other too close to that city, culture bomb and poof immediate available city. Btw early on, they have too few uses, mainly tech discover or ressource hooking.
So let's say :
early game is for : GS, GE, GP
mid-late game is for artists and merchants
As final decision i think GS are better than engineer game wise (i mean taking in consideration the capacity to get a specific people)