The general consensus seems to be that the ideal beginner razor is a 6/8 hollow ground round point. The reasons given are quite convincing: It offers a maximum of manoeuvrability while still being easy to strop (keeping a small razor flat can be challenging); it can take a decent amount of lather (which is an advantage, because the less you need to rinse, the lower the risk of damaging your razor by hitting the faucet); and, maybe most importantly, it makes it easy to watch the angle of the blade against the face.

This blade angle is one of the variables most overlooked by beginners. Let me try and explain taking an image by Bart:

As you can see, the angle of the blade against the skin becomes shallower with each pass ("TG" meaning "the grain", "W", "X", and "A" meaning with, across, and against, respectively). A wider blade will allow you to watch that angle more closely.

Unfortunately, the blog software does not allow for the insertion of flash animations, but if you are new, you should follow this link: http://www.pbjsite.com/shave/whiskarmap/preLoader.swf It is map of (your) face which you can use to track your beard growth, then assign certain shaving passes to certain areas of your face, then print it out and hang it on your bathroom mirror. Yes, it sounds silly, but it really is very useful. Here is the original thread for more background.

So coming back to size, and why it matters, I recently started using 7/8, and then 8/8 razors more regularly. First, because they present a nice challenge for your technique when all you have used previously are comparatively small razors. Second, because I like their looks. Here is one of my favourites, a 7/8 Flic "Prima" which I acquired from Smythe.

As you can see, it is very much the exact opposite of a razor I would recommend to a beginner. It is wide, has a thumbnotch and a relatively short shank. But it is very, very beautiful. So, yes, size matters, but maybe in unexpected ways. If you are new, make sure to eliminate as many obstacles from your shaving routine as possible. Wide, and therefore hard to manoeuvre, razors are one of them. Add a thumbnotch, and it gets worse. Add a short shank, and stropping becomes hard, too. So, yes, 6/8 full hollow round point.