I'm not going to repeat what others have said here, but the one option that neither 3speak or DTube seem to have (correct me if I'm wrong) is the ability to embed video on other platforms in the way you can with a youtube video. If I copy/paste a link to a youtube video in a Steem post, the youtube video can be played on my post instead of redirecting someone to another website.

While this might seem great to get people visiting 3speak, it's an irritation for the user who wants a seamless experience.

To be fair to 3speak, I am not certain how much the built-in features of a web browser play into enabling embedded videos, but if there is one feature that needs working on, it's the ability to watch a video from steemit.com or steempeak.com, rather than being redirected to another website. I want to watch a video from a steem post, not go to 3speak.

Just my opinion, but I believe between DTube and 3speak, the one to succeed long term will facilitate (in whatever way possible) the ability to watch videos from within a post. Even this post and your video redirect me to 3speak website, which doesn't make the experience seamless.