Ok lets look at numbers (Destiny)
Stats Courtesy of DestinyStatus.com
My PvE Kills by weapon:
Hand Cannon - 41.28%
Fusion Rifle - 13.43%
Auto Rifle - 13.15%
Scout Rifle - 11.89%
Pulse Rifle - 7.12%
Sniper - 4.46%
Rockets - 4.27%
Machine Gun - 2.42%
Shotgun - 1.97%
My PvP kills by weapon:
Hand Cannon - 22.53%
Fusion Rifle - 20.90%
Machine Gun - 16.16%
Auto Rifle - 12.91%
Pulse Rifle - 9.23%
Shotgun - 8.07%
Rocket Launcher - 7.49%
Sniper - 1.70%
Scout Rifle - 1.01%
So what does it mean? Well, I'd say generally it confirms that PvE is largely low level mobs with a few tough enemies thrown in which are easily taken care of by primary weapons. Special weapons are more often used in PvP. Heavy weapons play a much much larger role in overall kills in PvP, about a quarter of all my kills in PvP versus only 6.5% in PvE. So control that heavy ammo!
Personally it says I am a fusion rifle guy in both PvE and crucible (I am sure the mythoclast makes up a lot of the kills in PvE), I love hand cannons, and I get lots of kills with HMGs in the crucible.
Scout Rifles are more effective for me in PvE.
I am actually surprised that primary weapon kills make up the huge majority of PvE kills - about 73%. I guess Destiny is mostly about shooting weak dudes.
Now how boring was this?