Wih cage match the easiest to get are:
1. Shotgun (2)
2. LMG (3)
3. Sniper (5)
4. SMG (5)
5. Assault (7)
It's obvious, the less guns you have to go through the easier it is, sniper is easier than SMG because snipers are one shot kills so you dont have to spend 2 or 3 more seconds aiming again at the head and shooting, as you do with the SMG's. And you can shoot the other dude from further away and still get a headshot.
Without Cage Match
Easiest to get is very difficult for non-cage match, for many reasons, the shotgun, which only has 2 guns to get all the headshots with, but they are so innacurate, that you have to aim above the person you are so you have to sneak up behind them, which you rearly ever do... so shotgun becomes hard
This might help:
The easist golden weapon to get because it has the least guns to use. The number in [] square bracets is how many points it is awarded (will be explained at the bottom)
1. Shotgun (2) [1]
2. LMG (3) [3]
3. Sniper (5) [5]
4. SMG (5) [7]
5. Assault (7) [9]
What type of gun do you use the most?
Put it in ordeer, then put 1 point to the most used, 3 to the 2nd most used etc (like i did above)
What gun tpye (avarage) kills in the least shots to the head?
Sniper [1]
Shotgun [3]
Assault [5]
LMG [7]
SMG [9]
Now add up the points in the bracets (include the ones you should have put for the type of gun(s) you use most often)
The gun type with
LEAST points win

And that one should be the easiest/quickest for you to use, as you should be used to using them, and it won't be that hard for you to start using LMG's for example if normally you only snipe.
Best looking golden gun IMO is....
Assault
Sniper
LMG
SMG
Shotgun
I have had all the guns, and i found assualt the EASIEST to get, as just by using them a lot got it me, the hardest was the LMG's because i hated them, and when i played with an LMG i got really bad ratio then went back to assault/sniper