For me neutral sound reproduction is best. I have tried bass heavy headphones, bass shy headphones, headphones with elevated treble and headphones with elevated mid-range, but I still like the ones that are closest to the original sound best.
I listen to many genres. From nu-jazz to EDM, from J-pop to classical, from grunge to merengue. For my drum & bass collection, I wouldn't mind the Momentums because bass is a prominent part of that music, but for jazz the bass is often intrusive ans sometimes even overwhelming. With neutral headphones I can listen to any genre with pleasure.
A neutral, but deep bass is ideal for me, so neutrally tuned planars like the PM-3 are a good choice on that regard. However, the treble, and mostly the lower treble of the planars I have heard, sounds a bit 'plasticky' or 'artificial' to me. I don't know other way to describe it. A few people agree with me, but most are not even bothered by it. Compared to the elevated mid-bass of the Momentums it's a small issue anyway.
Many people prefer different types of 'exaggeration' of certain frequency ranges. Elevated bass is a common preference, so the Momentums fit that bill. Elevated bass and treble (V-shaped sound signature) is also quite common. Everyone has different ears, so to you the PM-3 might sound accurate, but boring. The first step to get a new headphone is knowing your own preferences.