It depends on your goals!
Some are saying how streaming on vimm.tv is much better experience, that might be correct - but they can't reward their streamers in a way DTube can (at least for now).
I honestly believe Vimm has great potential & it will develop, so I can see in the near future at least some kind of delegation heading their way
On the other hand, DTube is well established Dapp & they usually take care of all the problems related to their app, so if there is problems with streaming they will get solved (I didn't try it out yet)
If you keep in mind how they are a whale (1 000 000+ SP), they could be a better choice (at least for now) for new users to stream - since that kind of support will ensure them growth on the platform & allocating some SP their way
So yeah, it depends. If you are a millionaire & don't care about the money, then you can buy yourself 1 000 000 SP & support your streams on the Vimm network alone :D
Otherwise, I'd advise you to use DTube firstly or even better use BOTH platforms! and see how it goes :)