The flexibility is meant to conform to your mental image of the market.
If your mind has the market turning on its mark-to-market, then that's how you should set up your trades, and your brackets. If your brain is focused on a down-turn, and you're worried about what will happen to market psychology if the bid breaches a certain price, then that's how you trigger your trade -- putting it at an average or a last will not do you too well. On the other hand, if you wish to weather a spike down, then placing your TS with an average would save you from spurious bids.
So, what is your mental image of the market? Decide that, then configure your TS to match. (Each trade, each day, each TS.)