If you already have the shoes and pedals that work together, then use them. If you have issues that can't be solved with that combination, then you'll know that something needs to change. If you don't have the shoes. Which usually are the bigger expense vs pedals. Then it's not as big a deal whether you go SPD-SL or SPD.

As for shoes that handle both SPD and SPD-SL. It's still a matter of fit. So just decide which cleat method you want. Then buy the shoe that fits the best. Whether it's a double use shoe or not.

I'm SPD on my road bike and always have been since going clipless. I can't find a reason to go with SPD-SL since I don't compete with any but myself.