I don't think either is going to try to stifle the market..they're complimentary companies in the business sense; Curious Labs started the ball rolling (as I understand, they actually didn't make the original figures, but bought or licensed them from someone else), and DAZ has run with it. I think DAZ is offering a potential competitor, but neither is an absolute monopoly (we'll see where the business with Shade leads..;) on the figure creating or posing business.
I've never bothered upgrading to 5 (I'm still using 3 and 4..and have a lot to learn about both..;), and have played with D|S a little. There's a new interface to get used to, and I probably need to play with it some more (now if they would only leave behind the 'must render by date' concept for the addons, I'd be happier..;)
I haven't learned everything there is to know about either Package, but they both show promise..both are still in development, so they'll fix the old mistakes of the last ones, and have time to make new ones..;)

I wish I'd said that.. The Staircase Wit

anahl nathrak uth vas betude doth yel dyenvey..;)