SpriteMancer was born from Pixel FX Designer 2.0 and Juice FX 2.0. The 2.0 version of those apps will be discontinued as SpriteMancer is the same with the features combined. Juice FX v1.x will still be developed and maintained, so It's a matter of preference on which app you want to choose.
Also in case you missed it, If you have Juice FX you will see that SpriteMancer has a 100% discount, this offer ends this Sunday so be sure to grab it before It's gone :)