People here are making some commonly heard points about buying into a SYSTEM rather that just a camera, but that's only the case if you're really planning on buying a lot of equipment in the next few years.
From what it sounds like, you're probably better going with the a300 (which is a much better camera than the d60) and then in a few years switching over to one of the major brands (C or N) if you feel that Sony/Minolta is not living up to your needs/expectations.
My reasons for such a recommendation:
- I assume that you won't spend 1000's of dollars in the next few years on lenses and brand specific equipment (like flashes). If this is true, then you really are buying just a camera and not the whole SYSTEM (at least right now).
- If your uncle's lenses will fit the a300, you might already be off to a head start -- both in trying out new equipment, but at the same time, not becoming heavily invested in one brand (at least from your own money).
- If you aren't going to buy a lot of lenses, but do want improve your photography, one of the first lenses people will recommend is the 50mm prime. On the d60 this lens won't autofocus, and because the lens and the camera are physically small the ergonomics of manual focus are not the best. I have a friend with the 50mm on a d40, and he's thinking of getting another nikon (even an older d70) just for this reason.
- Likewise, the d60 is good for using a dSLR as a point-and-shoot (I recommend it to a lot of my wife's friends who want something for their kids' birthdays and such) but there simply wasn't a lot of real-estate left to put many controls on the body itself. A lot of the setting changes need to be done through the menu system (another reason my friend is looking to "upgrade" after only having the d40 for about 8 months).
- There has been more than once when I wished my dslr (Canon 20D) had an articulated LCD with live-view, for some tricker (above the head or down at floor level) shots). Also it lets you have the chance to get some nice candids by shooting from the waist.
- the 18-70 distance is a nice walk-around lens. 55mm can seem a little short in some cases. (neither is perfect, but the 18-70 comes a little closer).
- if you shoot RAW, there really shouldn't be any image quality difference between the two cameras. I think Sony makes the sensor for both (but don't quote me on that).
- I would love to be able to hunt down deals on older minolta lenses that still work with the Sony (and have "become" VR).
Having said that:
- the Nikon is a good camera: nice and compact; especially with a 50mm prime lens. If you left your camera home because of the bulk, you won't get any pictures.
- there is some evidence that in-lens VR might give about 1-stop better shake reduction than in camera; but you'll have to pay for it every time you get a new lens.
- In terms of quality, the Nikon kit is good for a kit lens. f/3.5-5.6 is slow but that's standard for this type of lens.
- Third-party lenses (tamron, sigma) will probably be released for the nikon before sony. The Tamron 17-50 2.8 is a great replacement to the kit.
- If my assumptions are wrong, and you are planning on accumulating a good deal of kit in the next few years, definitely consider the "whole package" and even map out a plan on how you'll grow your collection (i.e. making sure that you have the important distances covered without too much overlap, etc)
Either way, they're both great cameras, and the best thing to do is simple get started shooting (and a book or two like "Understand Exposure" will probably be the best bang for your buck, over any equipment.)
