Not knowing the pricing difference between the two and assuming they are similar, I would favor Backblaze as it would allow me to exceed the limit if I needed. Based on how you framed it, I would expect that with Wasabi you might hit a hard limit.
Wasabi doesn't have an egress hard limit and doesn't charge for egress. You get consistent pricing, and if you need to recover everything, it's not an issue at all, and you won't pay for it.
"The reasonable use egress policy indicates that if your monthly downloads (egress) are greater than your active storage volume, then your storage use case is not a good fit for Wasabi’s free egress policy, and we reserve the right to limit or suspend your service."
If you're using Wasabi for normal backup data storage, you shouldn't worry about egress. It is meant to prevent malicious users from uploading data and using up all the egress bandwidth, for example, a 500GB user egressing 5TB with public access or using Wasabi as a dump point to upload in one location and download in another region 1:1 ratio. As your storage goes up, your available consistent monthly egress goes up. It only becomes an issue if you abuse the account by uploading/downloading in a 1:1 ratio on a consistent basis.
What happens is you get an email from support asking if something changed in your use case. If so, they will help troubleshoot it(Think of a CDN scenario, where the CDN gets misconfigured). You also have an egress monitor for suspicious activity in case you aren't normally downloading all your data, and then you see a rise in egress https://docs.wasabi.com/docs/en/whats-new?highlight=egress#e....