Iron looks great but will need painting over the years. PVC is nice on a back deck but I'm not big on its use at the main entrance and focal point of a house. They can pretty much do with aluminum that the do with iron and it has little to no maintenance. We are in the process of building and going with Aluminum on both the front and the back of the house. Make sure you get a good quality and if you want I can check to see what brand our builder is using.
Here is a good link with what can be done with aluminum railings.
Aluminum Railing Details by RailingWorks