Probably silicone for soundstage. But if you're like me, foams or the (hybrid) "SYMBIO W Memory Foam & Silicone" are the only ones that stay seated, for any amount of time.Just got my FD7, already impressed by overall quality.
Which provided eartips go best with the large tubes for improving overall soundstage?
Most importantly, the ones that give you the best seal, without a great deal of discomfort.