If you're inclined to tinker and have the most basic soldering skills and some cheap thermal paste, you can pick up four or five different LEDs mounted to the copper boards from Simon for the cost of one S2+...perfect comparison platform. I think mostly you should decide if you want to try for a certain color temp, a little more throw, less throw and power for an up-close task or indoor light, etc. Keep in mind that you're a little limited with a smaller host like this both in terms of reflector size/depth and in heat dissipation. There are definitely differences in the emitters but I don't think you get to see the widest range of effects in a compact head like the S2+. Basically the larger the emitter die the less throw, all else considered within the same light design, so the tiny Osram is the standout and the older XML is the more floody (SST40 being the same size mostly). In a larger reflector you can get more of a variety. Personally my favorites are still the Samsung LH351D for general purpose and I do like the SST20 for stock higher current driver. I think the Osram isn't very useful in this small reflector size but it sure is impressive to see that little pencil skinny beam reach for the stars. SST40 kind of the same...in a small light with little heat dissipation potential you don't want to run higher amperage drivers so much so you may as well do the XPL instead (but certain uses like only brief need for the extra turbo lumens of a higher amp SST40 is both impressive and maybe useful for some things while still being in a tiny package). If beamshot pics and videos don't do it for you then there's one way to truly find out... :)
Edit: I don't know how popular the M1 is anymore but it's a considerable difference over the S2 head...reflector is wider and deeper and it's made for more heat while still being very compact and pocketable. Maybe one to consider adding to your mix either as a light or host to experiment with.