The saradomin mages are the easiest to kill, this is because using the correct method you don't take any damage. The best place to kill them is in the saradomin area of the god wars dungeon down the first rope. To kill these mages without taking any damage is simple, all you do is wait for them to attack the werewolf located in the same area. This then means that their attack is focused onto the werewolf instead of you. Only two of the mages will attack the werewolf, they are located in the east and west sides of the area. If you decide to attack the third located towards the south, you MUST use protect from magic. If by mistake, you attack one of the mages not already in combat, do not hesitate to use protect from magic. Sometimes you may also find that the werewolf gets trapped behind scenery in the area, if this happens simply lure the werewolf into range of the mages by attacking it and running so it can't attack you, it should then focus it's attacks on the mages once again.
Most people use melee to kill spiritual mages, range can be just as good though. If ranging using a fast weapon such as a short bow, throwing knives/darts etc perform best.