A couple of years ago, I was allowed to email a revise/resubmit directly to the editor of Spider. My email sat in spam until I status queried six months later. Fortunately, the editor received my query email and my story was accepted. Landing in spam probably doesn't happen often, but after that experience, my personal preference is Submittable. (Although truthfully, I'm about to submit another R&R by email to Ladybug at the editor's request. Crossing my fingers it doesn't land in spam.) You won't wonder if your manuscript was received or not. Of course, formatting is another issue, so you should do what works for you. This is just food for thought.