After a 2 year run with the iPhone 4 and switching to the RMHD about a month ago, here's my opinion...........
The battery on the Maxx is far superior. In fact, I have a hard time getting it to drop below 50%. I love the fact that I can leave all the extras on (Bluetooth, GPS, wifi, etc) without worrying about killing the battery. I had to carefully manage the system settings on my iPhone to get through a full day without hitting the charger. As a point of reference, under what is my normal usage, I went 45 hours off the charger with the Maxx and only got the battery down to 40%.
I have used my phone as an MP3 player as well for many years now. The head unit in my Jeep has built in Bluetooth and I always stream from my phone while driving. I've noticed that the stream from the Maxx is not only louder, but sounds much cleaner. I would get some occasional crackling with my iPhone. Everything sounds very crisp coming off the Maxx. I do miss the ability to dock my phone directly on the head unit though, as it had a built in 30 pin connector.
As for the radios, my Maxx CRUSHES my iPhone 4. I'm keeping a much better signal on the RMHD than I had on the iPhone. On a recent trip to a place I knew I loose all reception on the iPhone, I still had 2 bars of 4g signal. That's huge in my book.
Now the big one, the OS. Seeing how I also have an iPad, I miss the way that the iPhone and iPad worked together. The photo stream was a great feature. I find iOS a little more user friendly than Android. I'd consider myself more tech savvy than most, but I shouldn't have to think about how to make my phone do what I want. iOS was much more intuitive, in my opinion. It got even better after I was jail broken. Maybe it's because I'm still relatively new to Android, but I just don't find it as smooth or polished as iOS. Not that Android is bad, it's just different.
Just to be clear, I'm a fan of iOS and Apple products. In my house currently there is an iPhone 5, iPhone 4, two iPad 2's, and soon to be an iPad mini. When it was upgrade time, I decided I wanted something with a bigger screen than the iPhone 5 was offering, and thought I'd give Android a fair and honest shot. So far, I love the phone, and like Android.
If I could run iOS on the Razr Maxx Hd, it would be the most perfect phone in the world to me. That's my 2 cents. If there's anything else you'd like me to compare just ask. I have no problem giving you my honest opinion. Neither Apple nor Google are putting money in my wallet, so I have no loyalty to either of them.