Why not research each sub-specialty. If you don't know what they are, some include:
retina, oculoplastics, cornea, glaucoma, pediatric ophthalmology, neuro-ophthalmology. Other smaller and/or academic ones include ocular pathology, uveitis, etc. Possibly google these words?
If one is considering which one to do, interest in the subject matter should be the primary consideration. However, retina and oculoplastics is well respected and hard to get, particularly the latter. The others are very honorable, too (even more so if you have an eye problem. For example, if you have a neuro problem, going to a retina specialist isn't a good idea unless the guy happens to be very well versed in neuro).
