Difference between MK3S and MK3S+  

Is it worth it? I have not upgraded!

the + adds a new Supa Pinda, and a revised filament sensor plus clamps for the Y rails and Y berings, on to p of some easier to assemble modifications. 

If your Mk2S is running well, you will not see a huge differnce upgrading to the +

regards Joan

MK3S+

I have to agree.  I have replaced my Pindas slowly with Superpindas on most of the printers during routine maintenance, I have had only nominal improvement.  One the mini, they have made a huge difference, but the Mk3S, it has been a small change.  

Bearing clamps

In the past I've always noticed slight slack/wobble in the Y-axis. Maybe this was because I used Misumi bearings, but I think the U-bolts were generally not a great way to hold linear bearings. With the new bearing clamps, I can finally adjust the amount of compression evenly on the bearings to get the fit just right - smooth movement, zero slack/wobble.

There was also a revision to the extruder printed parts to improve airflow over the V6 heatsink. I'm not sure if this was part of the + update, or just a prior revision. You might find this useful if you suffer from heat creep, which for example can be one cause of bad tips with MMU.

Bearings

I don’t think it is the Misumi Bearings.  I have them and they work fine.  

Firmware compatibility

Someone can help me on this is very helpful for me, I have couple of MK3/S/S+ printers and having some issues on the printers while printing.  which firmware versions are most is compatible for each models  and I can use any slicer version to flash firmware process...?

RE: Difference between MK3S and MK3S+

this link identifies the latest firmware for each printer variant

https://help.prusa3d.com/downloads

you can use Prusa Slicer to flash the firmware the latest version is probably best, that can also be downloaded from the link above

regards Joan