Based on your edits... Firstly.. "What Chopper said". Secondly...
We're a VMWare ESX shop because that was the most mature product at the time we made our choice, and that is probably still true a lot of situations.
Hyper-V is a maturing product (certainly compared to VMWare anyway) that is still well worth considering, especially if you're an "all Microsoft" shop and are comfortable and familiar with how Microsoft like you to administer their modern round of OSes and apps.
For a testbed then I'd say that minimal stretch to learn the new platform is good, so if you're already very familiar with the MS infrastructure (and especially if you've already got the tools deployed that make managing hyper-v easier, e.g. SCOM) then this can be a good choice.
If you want to test a wide mix of operating systems from a more platform agnostic virtualisation supplier then VMWare starts to make more sense.
As for leading to production, both platforms are designed to integrate multiple hosts and shared storage for high availability clustering and other fancy features like that, which I'd argue is a good idea for a production network (virtualisation can mean putting all your (virtual server) eggs into one or two baskets (physical hardware hosts).
You have to consider the cost of a hardware fault that knocks 6 important virtual servers offline at that point, which makes the clustering features attractive. Clustering might not be cheap (especially as you need to look at shared storage to make it worthwhile) but on a production network not having it might cost even more, if you see what I mean.
If you think you'll go this way in the end, then VMWare have the more mature tools so it might be worth planning with the future in mind...