SPD-SL = Road use
SPD = ''All Around'' use (technically used for mountain biking though)
If you ride a lot in the city (frequent stops at traffic lights, etc.), I'd stick with SPD pedals & get the 2-sided ones that can be used unclipped on one side and clipped on the other one (Shimano PD-EH500 for instance).
If you're looking for optimal performance & comfort (especially on long rides & when climbing), go with the SPD-SL ones. This is what I have & wouldn't switch.
Also keep in mind that the SPD shoes will be more comfortable when walking, as the SPD-SL ones have cleats that are screwed under them (makes you look like a pengouin when you walk!).
It's all about your needs.
Last edited by eduskator; 09-05-19 at 05:48 AM.