I'll throw out my 2-cents regarding this question:
Starting at ArcPad 10 SP3 python will be supported as a scripting language in ArcPad. HOWEVER, there isn't (at this time anyhow) an official release of python which will run on a device with a Windows Mobile OS. So, for the foreseeable future, python in ArcPad will only be relevant on a machine running a desktop OS.
VBscript and Jscript have been, and will be, supported on Windows Mobile devices for the long haul.
You shouldn't run into any compatibility issues between versions 8 and 10. My suggestion is that if you've been using vbscript in the past, stick with it.