I agree with what you're saying. No one is completely trustworthy.
Assuming its pretty much comes down to a choice between Apple, Google and Microsoft though, and just going on visible previous track record, Google hasn't ever apparently done anything half as dirty as Microsoft or Apple already have in the past to their own customers.
I also like the fact that Android is based on Linux, (just because I like Linux) and I also like that the source for Android and most of its standard compnents is also open for all to examine (unlike Microsoft or Apple's os's), meaning they can't as easily get away with anything obviously aggregious, at least embedded in the core firmware. And if you found out they tried to, unlike Apple or Microsoft, with Android you can just install an alternatively sourced firmware or even build your own self-audited version.
That's not to say that I don't think Google would ever screw its customers given the right set of cicumstances, its just that they seem more aware of the large hidden cost of the inevitable discovery of doing so after a while than the others.
You have to remember that Google got where they were in the first place by at least apparently looking after its customers more than the others, mostly by giving a lot of actually very high quality services away for free as in beer.