Well... I think in gijoe's defense, for anyone that's never been to Japan (OP didn't mention, but just assuming) that may be a bit intimidating, even though it is very easy. But I would plan a bare minimum of 2 hours to transfer between NRT and HND, it is usually smooth sailing but you just never know.

But, if you've never been to Japan and have the time, why not do the transfer? Connections usually don't afford you the time to enjoy the city, but the bus ride may give you a tiny glimpse into Japan, especially in the HND area (nothing interesting about NRT's location) If I were you I'd do it just to be able to enjoy some sort of scenery.

Like others have said, HND has gone through some changes and has more to do. But in my opinion from strictly a connection/things to do standpoint, NRT is the way to go. Now if you were flying OneWorld into NRT T2 that would be a different story.... but *A, NRT is good.