Both are great for Steem. The two platforms actually have a different focus, although there is some overlap.
DLive was mainly set up for streaming, particularly game streaming, like twitch, although it also has a video section.
DTube was set up for videos, like youtube.
Both have large communities, with around 4000 or 5000 different users posting each month. This makes them the 4th and 5th largest platforms by "author" numbers. The streaming / video original focus makes the communities of the two platforms different, although of course many people still find the content through the steem "browsers" steemit or busy.
Both platforms have large delegations and the potential for new users to establish themselves and earn pretty good rewards with great content.
DTube is also good for curators since it has a curation scheme where it distributes a proportion of the beneficiaries percentage out to upvoters.
I would recommend trying them both and seeing which works for you.