Best way to manage big files downloads

I'm looking for the best way to manage the download of my products on the web. Each of them weighs between 2 and 20 Go. Each of them is approximatively downloaded between 1 and 1000 times a day by our customers.

I've tried to use Amazon S3 but the download speed isn't good and it quickly becomes expensive. I've tried to use Amazon S3 + CloudFront but files are too large and the downloads too rare: the files didn't stay in the cache. Also, I can't create torrent files in S3 because the files size is too large. I guess the cloud solutions (such as S3, Azure, Google Drive...) work well only for small files, such as image / css / etc.

Now, I'm using my own servers. It works quite well but it is really more complex to manage...

Is there a better way, a perfect way to manage this sort of downloads?