I would definitely recommend WeTransfer - especially the paid version. I feel like all of the shortcomings with the free service (file size limit & content deletion after 7 days) are all fixed when you upgrade your account, and the service is not very expensive. It only costs $12/monthly or $120/annually. WeTransfer makes it so easy to send files, and the additional features such as creating a link to your content & password protection are great. Very straightforward & easy to use.
WeTransfer is extremely reliable 99% of the time. There has been twice in 4 years that their service was unavailable due to server outage for several hours.
I've only reached out to WeTransfer support once, but they were prompt, courteous, and answered my question. I assume that future interactions would be the same, I'm looking forward to being a long term customer.
I did not choose to use Image Relay, the client did. I really like Image Relay and the fact that you can organize files in different folders, but not the fact that you have to create an account, have access to all the files and folders, and remind passwords. With WeTransfer skipping all these requirements, it is way easier and faster.