hi peter
windows 7 at release candidate stage is probally more stable than windows vista was at the same release candidate stage,so windows 7 is surely gonna be better than anything since windows xp
however windows 7 is also going to be significantly cheaper than vista was at release stage so depending on the upgrade cost to the end user it may be worth buying windows 7 yourself and installing it
the upgrade options that come with windows vista pc,s are not clear cut as they allways look,they may involve additional shipping costs and insurance and this can come to the cost of a oem version of windows 7 itself
for example i have found Microsoft Windows Vista Home Premium 32bit OEM with Windows 7 Voucher ( http://www.aria.co.uk/Products/Software/Operating+Systems/Microsoft+Windows+Vista+Home+Premium+32bit+OEM+with+Windows+7+Voucher+?productId=36920) and this comes with a form to apply for windows 7 however thats it!..nothing is said about how much it will cost
in regards to bugs well i am currently running the release candidate of windows 7 and as i have allready mentioned theres little if any bugs or problems,and compared to vista that was installed on my pc when i initially built it and it froze every day,sometimes 3 or 4 times a day,i originally thought the motherboard was the culprit however when i dual booted with windows xp and 7 no problems reported
so it just goes to show how bad vista really is,some end users like it but personally i think it should be laid to rest with windows millenium,another windows os that was very bad
pre-installed windows 7 would be fine however you would have to wait until xmas to buy a pc with windows 7,so the only option at the moment is buy a pc with the upgrade voucher,however be sure you ask how much it will cost and this includes postage,shipping and any other charges,otherwise it may be better buying a oem copy
alternatively windows 7 release candidate is still avalible at http://www.microsoft.com/windows/windows-7/get/download.aspx,and will work until august next year,thats a full year of windows 7 for nothing,worth a try
good luck peter !