Can't speak for the Nike+ one personsally, but I have read a lot of reviews that state it's less than stellar compared to Runmeter.
RM is ultimately completely customisable, offers maps, graphs and emailed reports of all your activity. If you have a Mac like me then it syncs directly to iCal too, so you have a permanent diary of your usage. At the end of each session it is easy to compare one run to any other from your history, by looking at pace, distance, top speed, elevation changes or any number of other requisites.
You can build an infinite number of activity types, with as many intervals in each one as you wish, plus record however many routes you like. You can have audible announcements at any interval (time or distance) you choose, that can read out any or all of the stats that are being captured.
Hope this gives a little insight. As has been pointed out, it IS iPhone only.
Well, Rumeter sorts all that out for you - you can set it to "stop" after your official distance for whatever activity you're doing (i.e. no need to touch the screen). I've been using it constantly since spring this year, and am still finding new features!
Reneroo, just to add an alternative (I too am looking at a Garmin watch in the future, as I am a big fan of their Sat Nav and GPSr units), but what app are you using on your iPhone?
I'm still using Runmeter, which I've had ever since I started "this" bout of leisure running, and it gives you loads of stats plus audible announcements at whatever interval you choose.
Just as an example, I have dozens of routes and activities set up in mine. This morning I ran a fairly easy 5K along a local route. Every 60 seconds I heard my total time running so far, my average pace, my total distance and my remaining distance.
You get loads of facts & figures at the end of your run, which can be emailed to you as a report if you wish.
Costs a lot less than a Garmin, and I have found it to be very accurate.
(I've also seen a lot of opinions on here and elsewhere that a mobile 'phone app cannot possibly be as good as a dedicated unit, but many of the people stating this opinion have absolutely no idea what these new applications are capable of.)