Ideally, you really inject according to the shortest Sustanon ester = Prop, which is why Sustanon should ideally be injected EOD. But, M,W,F is fine for convenience. Otherwise, blood test levels will be up and down.
Imagine injecting straight Prop once or twice a week. Would you do that? No. So why would you do it with Sustanon? You really would be wasting the Prop.
I used to use it once or twice a week and you definitely still grow, but that method's not ideal.