My opinion is maul or rigour. I say this because ccbow has +20 accuracy on the rune c bow, but not much else. Add that onto the fact that most slayer monsters have relatively low defense then I think you should definitly go for rigour first. As for which to get first, depends if you want to start range slaying right now, and if you plan to do a lot of dungeoneering. I'd personally say the maul, just because it's lots of fun and very good at TDs from my experience.