They are different, not really comparable, surely ?
One can have spiritual beliefs and yet remain secular depending of the job one is doing. Whereas agnosticism is a belief that the question is unanswerable/unknowable so it makes no sense to speculate.
Having no religion merely indicates there is no particular one, that one wishes to subscribe to/join. This maybe because one feels they all have faults, all the way across the spectrum to having never bothered to think about it.