Which one would you get?
Right now the Zebra looks pretty darn good to me.

If you want some reasonable responses to this question, you will need to provide much more information about what your musical goals are.  These are both excellent synths, but very, very different.  There's no way anyone could answer your question without a lot more information about what it is you're looking for in an instrument.

Depends on whether you're specifically after a classic synth sound a la Moog Modular or a general-purpose do-all synth. Diva nails the former, while Zebra is a Swiss Army Knife. Another difference is Diva is a heavy CPU muncher while Zebra is extremely efficient, allowing many instances even on a modest machine. Zebra is also due for a major update this year, and the upgrade cost is reportedly going to be very low ($39 IIRC).
 
Hive is another u-He synth that's been extremely well-received. I have no experience with it, though. The demos sound very nice, but it seems redundant alongside Zebra.

I'd go with Zebra unless you really want a vintage analog sound. If you do want that, or want really nice super saws go with Diva. They are both high quality synths, but their aims are different.

I will expand.
I am becoming very interested in synth programming and am a bit enthused with the modular concept of Zebra.  It appears intuitive and not as complex as Reaktor 6. I feel like I am in a Quantum Mechanics course when trying to use Reaktor blocks.
 I am also looking for dreamy , atmospheric sounds.
 
I hear lots of praise for Diva and see it comes highly rated in top soft-synth  categories. Just unsure which one I should purchase

They're both lovely... Zebra is awesome... BUT you really should buy the Hans Zimmer version upgrade, Dark Zebra, which gets you much improved Diva filters, many other goodies including 400 HZ designed patches...
 
For the extra hundred dollars you get a huge amount and it gets you Zebra 3 for FREE when it comes out... It will NOT be compatible with Z2 so you're getting the best of all worlds: the mindboggling flexibility of Zebra, the filters of Diva, and the genius of Hans, not to mention the free Z3... it's a no brainer. 

Let me just add my own experience: Diva is by far the best analog emulation I've ever used. If you're interested in creating the Moog or Juno sound (and quite a few others), this is the one to get. Nothing else I've found has the breath and accuracy of analog emulation.
 
I would also suggest you look at UVI Falcon as a possible instrument. I have Falcon, and find it excellent as well. I do not have Zebra II (yet), so no comments.

Thanks for the heads up for Falcon. 
Looks very impressive,  and this majorly complicates things.
I am on a quest for a new toy.

zebra is the more versatile, a real do-anything powerhouse/workhorse, whereas diva is an uber-analog emulation
 
actually, you should just get both

StuH
... I am also looking for dreamy , atmospheric sounds.

Zebra does this well. If you want to learn how to program them yourself, invest in one or more of Joseph Hollo's great patch libraries (Padsheaven 1-3) and pick them apart. That's how I learned to program Zebra.
 
Just to throw another monkeywrench into the works, somebody has to say it: the ultimate dreamy synthesizer is Omnisphere. Just sayin'.