it's not just a matter of preference. it's also a matter of what you need.
POD X3 Live
- more accurate and more comprehensive set of amp and cab sims
- works as a platform for guitar, bass and mic/vocals, with two of them simultaneously
- mature software support; works really well as a PC recording interface.
Boss GT-10
- more powerful and more flexible effects platform
- seemingly better build quality
- can work really well in front of an amp or the effects loop (or both at the same time).
- easier to get good sounds from (from what i've experienced, at least)