This is a pure optimisation problem. It depends on many factors like:
- What you need to do with the tween
- How many different tweens you need to calculate
- How much signaling between systems you need
- Whether you need to use that data in your CPU bound process or not.
- How much time you have to write the code
- What your tool set supports easiest
See if you only need one value to interpolate then your CPU is more than likely faster (unless you're running some weird embedded system). Even if you move a bunch of points you can still calculate the tween of that one position and do the needed cluster transformation in the GPU, like bone animation.