One is like a boob tube but lacking the secret porn stash.....other makes you go gaga Live :D
Nah seriously, Dtube is like the Steem equivalent of youtube just without the advertising sponsors (yet) and the censorship, however it does have some massive delegations of a few million Steem Power from Steemit Inc, so if your stuff is good - yes it has to be good like ComedyOpenMic winning videos entries good then you'll get fat upvotes, or if you're a famous YouTuber that Dtube is trying to lure, you'll get favoritism and lots of upvote love too. It's great for consistent high quality video posters. :P
Dlive on the other hand can work like twitch, has live streaming features, and it also has massive delegation from Steemit Inc. It's Steem Power is mostly used for spreading out smaller percentage upvotes to a larger number of Steemians who do vlogging. Some of the live streaming are also done with Discord voice discussion, so it is a bit of a favorite with various Steem communities. Use Dlive if you're starting out and if you just want to record your stuff live.
Dtube charges you 25% of your upvote bounty, but it also pays upvoters a share of the profit which in time could encourage curation, and Dlive is currently free to use. Loads of other differences, but this is a nutshell.