Okay so I have to say this since it's something that is discussed and I want to give my view on it. I feel Demon and god slayers are equal in power personally and that dragon slayer magic is tailing them pretty close. We know that Demon Slayers are much stronger then Dragon Slayers because when Grey's father froze the village Natsu's Flames couldn't melt the ice or even scratch it telling us Demon Slayer is stronger. Now when Natsu was going up against the God Slayer he had a hard time and only won due to clever thinking while the God Slayer obviously had more raw power. Now think about how the Slayer Magic Element Matters and no I don't mean water vs fire but more as Natsu is beyond strong due to his anger and wrath which makes his flames burn hotter and how Gajeel is extremely strong willed and hard headed which causes him to be stronger as an Iron Dragon Slayer. So if you look at it the God Slayer Natsu fought wasn't as strong as he could have been due to his personality not fitting his element. So I'd say God Slayer and Demon Slayer are equal and Dragon slayer is right behind them if all of them are at full potential.
What do you think?