For those of us who don't race and don't ride on the highest or near highest level, it all comes down to if you need to walk in those biking shoes, and walking here doesn't mean any long distance but even just ten, twenty feet, or indoors on just about any surface.

Another factor is a fashion thing, if you mix with road bikers and would mind them looking down on your pedal choice. If you are the type who wants to belong, do things the way they are supposed to be done, then go for SPD-SL

Bottom line is, either choice won't make you faster on the bike (or only marginally faster to a point where it doesn't mater), it is all about what one wants apart from that.

I have two shoe pairs, those that I use for summer riding can mount either cleat type (I use them with SPD cleats) and those (because they are universal) I can't walk in them.
The other pair for spring, fall riding as they are warmer type, have also normal sole and so have only SPD cleat mount and can be walked in fairly reasonably. I only mention this because I know how it with both shoe types, road of MTB style.

Last point, get double sided pedals (if choosing SPD). Single sided might look more in line with road bike as pointed out above, but are PITA