Streaming videos are videos that can be looked at only on the website. For example on the Dan And Dave site on your account dashboard there are the streaming videos that you can look at only on their site. Downloads are videos that you have to download onto your computer and take up memory. Hope this clear things up
Streaming is like watching a video on YouTube. Downloading is well... Downloading! This will take up some disk space and you'll have to wait until the download is complete in order to watch it, but once it's on your computer, it'll be there forever (remember to back-up!).
I personally prefer downloads, but that's just my personal opinion.
Streaming is quite possibly the way of the future in that many people who pay and "download" something typically tend to "share" it with friends or they all chip in and just keep making copies of the file. Is it wrong? Definitely.
I do see how some people dislike streaming because they don't feel they own a physical tangible item that they paid for and there is the uncertainty of "what happens" if that particular site closes up shop?