Depends on your speed/closure/relative E states and whos driving the Spit.
You have two options:
- going down with him. Follow him in the SplitS, chopping throttle and dropping flaps to help you make the loop as tight as possible. This is only recommended if your closure isnt too fast (that means youre not much faster then he is) and when you are sure youll be able to follow him. The danger in doing this is that you gain too much speed on the way down and due to that and your lower maneuverability your loop would be much wider then his. This can result in a flight path overshoot and get you killed quickly (depending on if the Spit driver knows what hes doing)
- the second option is not to follow him down (duh!) and to go vertical instead. reposition above him, reevaluate the situation and then renew your attack. This is the "not staying in the saddle for an immediate kill but playing it safer" option. Since hes doing a SplitS and you stay above him (immelman/climbing turn - depending on speed) he will loose more Energy compared to you. Also, you keep the positional advantage on top of him.