My Opinion.

Defensive wise;
Long Lasting Smoke Bomb - Stops the Attacks in place to buy some time for VIP to escape.
Strong Charge - Counters a lot of abilities and takes down the Attacker just out of reach.
Mute - Halts the Attacker for that second before they can assassinate, giving you that quick chance to stop'em and/or save the VIP. (Tho this is harder and more riskier.)
Templar Vision - See the attackers coming and warn everyone on your team. Warning, this requires communication with team mates. lol

Perks-
AutoBash
Overall Cooldown

Offensive wise;
Disguise - Sneak in and take out the VIP.
Hidden Gun - Pick'em off.
Charge - See Above.
Smoke Bomb - See above.
Firecrackers - Blinds'em and rush in for the kill.
Throwing Knife - Slows down the VIP from escape.

Perks -
Chase Expert
Auto Bash

Again, just my opinion. I'd recommend select what best suits you.