First : what do you mean exactly by "storing" ?
A short answer would be : I would use NO cloud service to keep my files safe and definitively use local hard drive/Nat server.
A longer answer ^^ :
maybe check if your password is not already leaked (Anyway change passwds every 3 months
)
ie this post links to a 3GB file of cracked passwords, fresh from last september ^^ :
https://cracked.to/Thread-MEGA-Entire-DROPBOX-LEAK-4GBs?page=1
I would never use dropbox, googledrive, onedrive or any of these well known Grand Public service for anything more risky than holiday pics shared with my familly, using a private mail.
OR delete your files as soon as your customer got them (even if you think gaining time to upload...).
OR consider a real professional (paying) service.
Else, you can check to temporary share big files or folder and keep them relatively safe by using "lightly less well known" ones:
pcloud: 'best cloud of 2020'... I didn't really checked yet. Seems nicely secured but start plan begins at 10GB only (a new 'box.com' ?)
megasync: many models use it it seems to share/send videos, but i don't know it so well.
box.com: (I use to share big projects with customers on this one). Start plan, is 10GB only, paying for larger space.
1fichier.com (aff link in my signature ^^): a nice system of "credits" can be used to extend your storage space. Start plan of 1TB for free (hugely used to share movies....)