I've been looking at rendering better eye glints without using painted glints onto eye textures. I don't think I have any definite answers, but here's what I have learned so far.

The test bed for all these images was V3 with the DAZ medium-res textures, a single infinite light casting equal light on both eyes, and the Front camera used for renders. In each case the cornea material was altered to make changes. Using the specular channel only, I got these results:

The default settings are useless - the highlight is barely visible and the eyes look dead. It's possible to increase the highlight size, but that doesn't really help and the specular value needs to be higher. By turning down the size, and upping the specular value, you can get small bright highlights, but increasing the size makes the edges softer, which might not be desirable. In the end I settled for the final render as a comparison, keeping the left eye at these settings for comparing with the various specular nodes in the right eye.

The next image shows the effect of the specular, blinn, and glossy nodes plugged into the alt-specular channel of the right cornea.

Note that the specular node with a specular value of 3 and a roughness of 0.1 gives identical results to the specular channel alone with the final settings in the first image, so I didn't look any more at this node. Blinn in the default settings gives no highlight at all, and I had to turn the specular rolloff right up and increase reflectivity, too. The eccentricity needs to be very low to avoid completely blurred highlights, but with a low eccentricity you get a very small highlight. In the end it's a trade off, and the two blinn images show the difference in eccentricity with other settings the same. The glossy node is interesting because of the sharpness attribute but if this is turned up too high, the edge of the highlight is jagged. The default size is OK, but the brightness needs to be turned up with the Ks setting.

Finally, there are the phong and anisotropic nodes:

Phong doesn't seem very good here. To see it at all the size and specular value need to be turned right up and then the highlight appears to be too 'high' on the cornea. Anisotropic produces non-regular shaped highlights and if you increase the size the specular value needs to be turned up as well. But it does give nice, hard-edged highlights.

So which gives the best results? It's not clear-cut from these short tests, but phong doesn't look helpful and the specular node gives the same results as the specular channel alone. I prefer the blinn node with a small bright highlight, but glossy could also be useful in many cases.

Sorry about the length of this post - hope it's of interest.

Steve