An obvious aspect before the upgrade; what you would have to pay? Up to the end of Jan, 2013 there are attractive deals for you from Microsoft regarding Windows 8 Pro upgrade. You can opt for upgrade for just $39.00 up to the given date.
However, we don’t know the price after the date but what we know the price of Windows 7 upgrade which was approx $160. So, time matters a lot for the upgrade; count it.
If you are buying new PC/laptop
In the case you should opt Windows 7 first and then take the benefit of cheap (just $14.99) windows 8 upgrade. Actually, we have users reporting some problems with Windows 8 PCs so I won’t recommend going directly with Windows 8 in case of new PC or laptop.
If you are buying a touch gadget
However, if you are well minded to purchase a touch gadget then I would recommend you to directly go with Windows 8 since this latest OS from Microsoft is well optimized for touch screen gadgets.
Actually, if you buy a PC or laptop (even having touch facility) with Windows 8 OS then the hardware drivers will be Windows 8 compatible and you could not downgrade to Windows 7 later on if you experience some problems.