I'm 72 Slayer with 94 Attack, 98 Strength and 83 Defence. I'm currently using Duradel in Shilo for tasks but I'm starting to get fed up with how repetitive he is, I haven't once had some of the tasks (e.g. Dust Devils) and I keep getting the same string of tasks, Greater demons, Mithril dragons, Waterfiends and Black demons.

 

Would it be better for me to go down to a lower slayer master til 75 or should I stick it out with Duradel? Is the EXP that big of a difference?

I would just stick with Duradel. Always use the best Slayer master you can use. However, if you find him still too challenging, you can always get tasks from Sumona in Pollnivneach.

I would stick with duradel and if you really dislike some of the tasks perhaps spending points to cancel them would be wise. If you really are starting to hate slaying with duradel you could use Summona for a number of tasks however I would strongly urge you to use Duradel for your 10th task bonus.

Stick with Duradel until you unlock Kuradal and also do Smoking Kills for the Slayer Mask and to block those irritable tasks.

You really should stick with Kuradel.

It's funny that you want dust devil and etc but honestly, you're complaining about some of the best tasks out there.

Black demons and greater demons are extremely fast (good charm drop as well). Waterfiends are not the fastest if you're doing them in AC but they're amazing charm droppers. I've never even had a mithril dragon task :P

 

If it makes you feel better - I've been getting dust devil tasks. They're not extremely slow but they're not fast either. They also don't drop anything at all.

Stick to Dura and at 75 you can switch over to Kuradal.