Hi John,
I shoot with a Sony A300 and do love it. The live view is excellent and the moveable lcd is very good. I have not used the two cameras you have mentioned but did try the older nikon when buying my first DSLR.
I totally agree with Chris' advice about going to a shop and having a hands on play. This is the most consistant advice I have seen on the forum and think it a very valuable lesson. Find what fits your hands, for me the sony A300 was spot on however have recently tried the new sonys and their ergonomics don't fit as well. If the shop has the A350 this is also a very good sony and is a little bigger but a great sensor.
Old minolta lenses are a great way to get 2nd hand lenses for sony,
www.Dyxum.com is a great community to get a view on sony/minota cameras and lenses, they have a lens database for usable lenses (A great help). I am sure nikon have simular communities.
Just try them out and find what suits you.
Tom