My approach is and always has been go with 7 unless your PC is on or near the lower end of the requirements - in which case stick with XP. Benchmarks I've looked at in at least 2 reputable magazines back this up - and chances are if your PC is fairly low spec you're not going to see loads of the windows 7 advantages anyway.
I don't even see how this is is an argument. XP has a couple of features and lower(read: old) system requirements, versus Vista's much more secure and stable platform, and quite a few new, useful features. 7 Just improves on that.
Honestly, I think the only reason people hate Vista so much is because they can't see under the hood. It did terrible launch as well, which contributed to this, but so did XP. The key difference is that the advantages of XP over 9X were very clearly visible....not so in Vista.
I completely disagree with most of this. Vista's much more secure and stable platform? If by "much more secure" you mean UAC then I see where you're coming from - but it most certainly doesn't make things more secure. Sure, theoretically it's great but when users just get into the habit of clicking "allow" whenever a box pops up, that's what they'll do. It's a bit like the security bar in IE6 designed to stop malicious activex controls and suchlike being installed - great in theory, completely useless in practice (and quite frankly I'm surprised Microsoft repeated this mistake with UAC!)
As for Vista's stability - well let's just say it doesn't seem that way to me. Slow and bloated are the words that come to mind here, it consumes stupid amounts of resources and really does pretty little with them. Sure, on newer flashier computers that's not an issue and sure you can hack down unnecessary services and turn off things you don't need to speed things up. That's not the issue as far as I'm concerned though, the purpose of an OS should be to do its job and use the minimum amount of resources possible to do it. I've seen Beryl + Gnome + Gentoo running with full 3D effects on a GeForce 2 MX with a PIII under 500Mhz. Put Vista on a machine a machine 4 times as powerful as that and it'd hugely struggle.
As for XP being good or bad when it was first released - that's not really the issue here. Vista actually turned out to be a bit of a mixed blessing for XP, simply because it was so delayed Microsoft were forced to maintain XP as their primary OS for many more years than they thought. As such it's been constantly improved, secured and updated and is now a pretty mature (and generally good) OS. If anything I'd say it was likely to be MORE secure than Vista or 7 - most businesses round the world use it and as such it's been tested rigorously. The other two, not so much.
While it's no custom built linux distro for speed and efficiency, 7 most certainly does improve on Vista and does improve on it well. Windows is never going to be as slick and as elegant as some of the open source variants, but keeping it in context it has done very well - I applaud Microsoft for taking a step back and slimming things down rather than doing their usual "let's cram as much crap in here as we can" trick as of late.
So yes, I do think 7 kills Vista off and apart from any obscure compatibility reasons there's no reason I can think of why anyone would use Vista these days. XP however is less clear cut - while I wouldn't recommend using it straight out for new installs because of its age and lack of likely support in the future, I would still recommend it on older machines. I'm still using it on my laptop and probably will for a while yet - it does everything I need to and as far as I can tell, does it well.