Here's a video of the different smashes. Phone camera is all I have, lol:
https://www.youtube.com/watch?v=4Ot-lbV4QFs
Technical difficulty goes up as you go down the list, but nothing is really very difficult.
1. Standard f-smash. simple enough.
2. Stutterstep fsmash: slightly more distance by canceling a dash startup into a smash (I think).
3. Pivot fsmash: LOTS of extra distance, just make sure to input the two movements very close together. It's pretty tight.
4. Stutterstep pivot smash: LOOOTS of distance, basically a quick dash dance into fsmash. To get the max distance here, you need to dash as long as possible while still being able to do a dash dance. I mess it up the first time and get just a little distance, but the next two go quite far.
Not sure if it's any faster than wavedashing or wavelanding into a smash, but if you're going to do a grounded fsmash the extra distance (especially on 3 and 4) can really help.