Both do the same job with few limitations,
Based on number of clients SEPM will need space to keep the definitions, database and log files.
If you are opting for cloud you dont have to worry about SEPM, coz SEPM is Hosted.
If you are having less number of clients say less than 10. Install all the clients as unmanged, set a liveupdate schedule, set a scan schedule. all will work just fine.