From my experience playing Spartan Ops solo on legendary I can say the following:
Spartan Laser: It takes 2 shots to take down a Hunter. You may be able to kill them in one shot if you can hit them in their back portion (just below the armor), but I haven't tested this.
Fuel Rod Cannon: It takes 6/7 shots to take down a Hunter depending on where you place the shots. Shots landing directly on their shield seems to slightly reduce the damage dealt.
Plasma Grenade: It takes roughly 6 grenades to take down a Hunter. I imagine the Frag Grenade has a similar requirement.
Rocket Launcher: It takes 2 to 3 shots to take down a Hunter, again this depends on where you land the hits.
Sniper Rifle: In previous games it took 2 direct hits to take down a Hunter (those are hits that hit their 'orange' area. I imagine it is similar in Halo 4, although I haven't confirmed this.
Shotgun: It takes 7/8 shots to take down a Hunter. These shots 'must' hit their orange area. My tactic for this is usually as follows: practically hug the Hunter while it's facing you. When it does it's charge / slam attack, jump over it, quickly turn around and shoot him/it in it's back just below the armor. At this point you have to quickly be aware of their backwards slam strike. Again, jump over it or strafe to your left/right and shoot in their back again. Rinse and repeat.
This tactic basically applies to any non power weapon. You have to keep them close to you so they can expose their non-armored areas. If you maintain a certain distance from the Hunters they'll constantly 'hunker down' making it very tedious to kill them. This tactic does require a bit of practice on the timing of your jumps and/or strafes.
Sticky Detonator: It takes 4/5 shots to take down a Hunter: This clip greatly demonstrates how you should do this. Stick them on their heads, detonate. Rinse repeat.
One other, more general tactic ( any weapon ) is to use the Hologram armor ability: Allow your hologram to grab the Hunters attention and then quickly land a few shots in the back while it's facing your hologram. This tactic does take quite long though.