I've had formatting go askew on the same version of Office on Windows without involving any Macs. Office isn't very good at preserving layout, that's not its job.
Office is probably your best option if going for one or the other. I use Pages and Word in tandem, for similar compatibility-optimising reasons, and while I prefer Pages for creating the text and for the bulk of the editing, I use Word at various editing stages for when I need to exchange such files with Windows users. It's not a perfect system but with some manual adjustments here and there, it does do the job.
As the earlier post suggests, Word has invariably had compatibility issues (even with other Word versions) and, in my opinion, Apple's iWork/Pages predecessors, AppleWorks, and especially ClarisWorks were better at dealing with Windows compatibility than the current Pages.
I've used this dual-program system for a good few years now and while not quite as smooth as it once was, it's still better than working in Word all the time, I reckon.
If you find you prefer to work in Pages, and you do a lot of word processing, then you too might find a way to combine both programs to good effect. Others may offer other differing but similarly positive experiences and ways of working.
I can't really speak from any experience in respect of PowerPoint and Excel but I am aware that working in Keynote can lead to compatibility problems when PowerPoint is involved at the end-user stage.