The great spy is generally the best for settling.
Settled the base yields are:
Great Spy: +3
+12
Great Artist: +3
+12
Great Scientist: +1
+6
Great Engineer: +3
+3
Great Merchant: +1
+6
Great Prophet: +2
+5
Generally, it looks like the artist is the weakest to settle except when you're going for a cultural victory. Outside of future legendary cities, culture points don't add anything to your economy or victory unless it gives you your first border pop or makes the difference between having control over a tile. In that case, I say, why not declare war and take it by force? And when the AI builds cities 3 spaces apart, the instant, revolution-independent, multi-border pops aren't that big of a deal.
The way to make the settled great persons equal would be to assume that 1
=1
=2
=2
=4
=4
Though even given that, the great scientist and great merchant are worse to settle than the great engineer, great prophet, or great spy.
But my next question is: Is
really worth half as much as
when you can get an equal or better research yield per point with
? Furthermore you can get better multipliers for
with less investment, which I suppose makes up for having to build spies. It looks to me like the great spy has the best yields.