I was thinking of getting DFS but it useful for slayer and bosses and dragons but I only using it for training not on dragons so shall I just use Rune Defender or Dragon SQ?
having both is good but for training its alright but i would recommend that you use the rune defender if your training with whip
If you're training strength, go with your rune defender, as rune defender has one of the highest strength bonuses you can get in your shield slot.
if you're max combat going for 99 slayer use defender, because the only upside to dfs is def bonus, the str bonus on defender is better then dfs and will make you hit higher. i use defender over dfs in almost all tasks, it helps me finish task faster ^_^