Personally I like a nice long range sniper kill so mine would be:
Name - The Key [quote]anyone got a better idea?[/quote]
Description - "That round fits quite nicely..." Unknown hunter
Attributes - 4 round sniper rifle, damage model of icebreaker and patience and time, slowish reload, minimal recoil.
Perks would include standard flared magwell to increase reload, field scout (ammo goes to 6 instead of 4), firefly (enemies explode when killed with a precision shot)
Exotic perk - Keyhole (After killing an enemy with a precision kill the next 2 rounds in the magazine deal solar damage, 1.8* as much damage as normal shot and have a 15% chance to return a full clip to the weapon after the two special rounds have been shot)