The last point made by VLouis is the critical one. If you want to be able to access the HDD using both LibreElec and Windows then, unless you have a high speed network, you really have to stick with NTFS or ExFAT., otherwise, if you use EXT4 all Windows access will have to be via SAMBA or something like FileZilla.
A lot will depend on how you load stuff onto the HDD. In my case I'm back to using NTFS after a time using ExFAT. I started with NTFS and moved to ExFAT because of the corruption issues (not real corruption ie I never lost anything but LE/Kodi wouldn't boot with the HDD attached). I moved back to NTFS because with one of the upgrades and the move to RPi4 the way file timestamps were calculated on LE and Windows differed which messed up my backup system.
I'm not concerned about the time to move a ripped DVD over to Kodi over my slow network I just wander off and let it get on with it while I do something else, even if it takes an hour. However, when I moved from NTFS to ExFAT I connected both live and backup HDDs to USB3 ports on my PC and it still took 10+hours to copy the c3.5TB of data. If I'd tried to do that over my slow powerline LAN it would have been in the DAYS.
With that out of the way I'd like to say that using ExFAT did give me a lot less problem on LE/Kodi. There was only one big issue. If I tried to boot my Windows PC with a 6TB ExFAT formatted HDD - it just wouldn't. Whenever I forgot it (my backup HDD) was plugged in I had to turn the PC off, unplug and restart. Not a problem with NTFS.