It is clear that Vimeo is not a good hosting option. I switched at the worst time but it seems like they had a big issue last year. Amazon is what I had been using but it is too whacky on the charges. What is a good and RELIABLE option?
As @mosafer said, you should definitely consider a CDN (Content Delivery Network). If you anticipate lots of concurrent access to your channel, a CDN will insure that the performance is optimum. If you do not use a CDN, and, you have lots of access, you run the risk of constant buffering. That's something your viewers will not like, and, will simply result in removal of your channel.
As far as a what to choose, that depends on your budget. I've been using Amazon S3 with CloudFront and can't complain. Sure the cost varies each month, but, it's based on the amount of access to your channel. You'll find that is the case with most reliable CDNs.
Good call on the UCDN. I just started using them. The ability to connect them to my server and cache and serve up HLS for videos is so simple to setup and use.