I need some advice on keystones for Midlane Lulu

I'm really torn on what to use for her. Deathfire Touch is actually quite nice because she can proc it quite reliably but you really don't notice it's effect until like mid-late game. Stormraider's Surge is really nice and allows you to use W on enemies freely without missing out on the MS boost for a self cast. Thunder Lord's Decree is nice as well but you need to be in AA range to get the proc on it, and that's no place to be in teamfights. Windspeaker's is quite powerful but doesn't work for self-casts so does nothing to help your laning. Decisions, decisions.