Slayer staff is the best weapon by far to use on a 1 attack strength pure, but it requires 55 slayer to use, which is a huge pain to get. It's definitely worth it though if you're going to be training up to higher levels. Otherwise, the event rpg or red topaz machete would be best up until 60 strength (not sure which one is better, I'm leaning towards the rpg), at which point you should switch over to using an obby maul with a berserker necklace.