I have the rb-s with a50mmm-65mm-90mm-127mm and a180mm all are C lenses.
I find myself useing the 65mm more than the others but I take a lot of landscapes.
The 50mm is not as sharp unless stoped right down IMO.The 127mm is good for all
body shots and the 180mm is great for head shots but can be a little heavey when handheld.The 90mm is a great allrounder and is especially good for macro when used with the extention tubes.
I also have the manfrotto 055 which is very versatile and suports the rb with out trouble.
I keep all my gear in a lowepro dryzone 200 especially out in the field because
it don´t like wet conditions the lenses lock up when wet.
I hope I have been of some help and have a great RB experiance it is a wonderful
tool.
Regards
Stuart.