[cbarrrr]

Looks and styling are subjective and no doubt play a big part in most peoples preference between the two. The riding position on the F is more upright but the R is hardly a supersport position, it's still a small bike mainly aimed at new / young riders and as such the riding position is forgiving. I found it comfortable on long rides.
Apart from looks, the main difference to consider is that they are naked or fully faired. Being faired makes a big difference to wind buffeting and affects my riding experience and pleasure on long trips. I currently have an MT03 and even though I love it, I don't think I would buy a naked bike again. Where I live R3s are about 50% more expensive than MT03s, if they were the same price I would have bought an R3. Just my 2c.