Some folks will likely put up a list of obscure features to try to differentiate the two, but they're pretty much the same feature-wise. My advice is to pick them each up and play with them. See which sticks you like better, and which radio feels better in your hand. If you intend to use it for a long time, take the time to see how they each feel. Buy whichever works best for you.

For me, it was an 8103 over an 8U. There was a distinct difference in a feel/quality sense.