There was a thread on this subject, with branches into S lenses on SL and R macro lens choices, but that was long ago, so...
I have had a "pre-owned" APO-Macro Summarit-S120 with an S to SL Leica adapter for about a year, and recently got the APO-Macro-Elmarit 60 CL and have been using it extensively (it's wildflower season here). Since our little pear tree is in the middle of its brief show I decided to try both sets of gear on it. I'm most satisfied with the result obtained by the Summarit:
S1010653 by scott kirkpatrick, on Flickr Summarit-S 120 @ISO 320, f/16
But that was after shooting the same branch with the CL and reviewing, then modifying the composition and exposure slightly for the second try. The most comparable CL shot:
C1030155 by scott kirkpatrick, on Flickr CL 60, ISO 500, f/8
Autofocus with the S/SL combination near its minimum focus distance is fussier than with the CL. These were taken hand-held. Each blossom is a bit under 2 cm across.
Both lenses have their strengths, but if the lovely blossom is more than 500m from the car or house, the choice is clear.