Damage over Time Multi vs Fire DoT Multi

Hi all, first league in a few years so decided to go with the uber safe and awesome RF Jugg to ease me back in.

Trying to work on my sceptre. I currently have FDoT on it but there's one in the market place I have my eye on that's better but instead of FDoT multi it has just DoT multi.

before I drop the currency: What are the differences in terms of how powerful each one is relative to the specific RF build? Will they do the same job?

Also same question applies for "elemental damage" vs "fire damage"?

And finally a bonus question if you don't mine. Is % spell damage applicable to this build? Is it buffing RF and is it a good modifier I want to prioritise?

Thanks in advance

Muchos gracias my friend :D