carbon or other
technicaly carbon forks offer a better and smoother ride as they absorb more surface vibration so give the rider less fatigue through the handle bars.
manufacturing in carbon is always more exspensive due to the labour cost of layering and materials, however the plus side is more functional shapes can be made i.e aerodynamic (lowering / reducing air resistance).
cro mo forks would generally offer a more rigid ride as they absorb less vibration and you can tell the differance in ride quality between both materials.
cro-mo will always offer the buyer a wider range of choice bewteen brands as carbon options are limited to 3 or 4 manufactures.
it is true that carbon is sometimes seen a fashion thing but it is also very much functional as well. a weight saving is also a plus but with some cro-mo forks getting lighter it will be grams rather than pounds that are saved.
i have riden both carbon and cro-mo and would say that start with cro-mo and move upto carbon making your bike a much better machine as your riding improves.
thats pretty much it