I'm quite new with FME and working with coordinates. I'm trying to use the AttributeReprojector transformer to convert NAD27 Lat/Long coordinates on my features into WGS84 Lat/Long coordinates in my workspace. I'm having some difficulty with selecting one from the many choices. The question I have is when I open the Coordinate System Gallery to select the coordinate systems for the transformer parameters, I see at least 3 choices that look similar to me for WGS84, ie they use the same datum, units, projection and ellipsoid. Does anyone know what the differences are?

Question 2: For NAD27 it seems another step more complicated. I'm having some difficulty figuring out what the differences are with so many choices. Eg is there a difference between all of these NAD27 datums? Can anyone point me in the right direction? Thanks in advance.