I believe the most efficient way is not to just raycast with the whole workspace, evidently, but
perform a Region3 check around the character to whitelist nearby parts as that is more efficient? Supposedly. At least, in the result of using it to whitelist, and then raycast with that whitelist. Idea from @XAXA.
My question is why is this the best, and if not, for this case what would be?
Region3’s tend to become laggy depending on how many parts are in it, how big it is and a few other factors that I dont want to mention because im not entirely sure what they are yet.
A Region3 is mostly used to detect when a player enters a new region for example or when a part enters its next destination.
Raycasts on the other hand are usually used for weapon systems, hacky tactics and anti cheats.
You should be including multiple checks in your script to detect what platform is under a player like checking their floor material and such.
If this is already something that you have been doing then I think your script should be as efficient as it is already.
If you do however want to find a more efficient method you can experiment with many of the built in roblox functions. (Thats basically the point!)
Hope this helped! 
