Well with cameras today I think it's generally safe to say that there aren't really any bad ones out there any more. Having said that people still generally stick to the 2 "top" brands that are Nikon and Canon. There are various reasons for this, quality construction, after market support, lenses, software, features, etc.
When it comes to sales people.... he either really believes that the Nikon is the better or what is often the case but not always... he's getting a higher commission on the Nikon so he makes more money from you choosing it.
The first thing that i always advise when choosing a body is to clear your head of everything you've heard about the brands.... and then pick up the bodies and have a feel. If the Sony and the Nikon felt better to you, that's all that matters because at the end of the day, it's YOU who is going to be using it and not anyone else.
Having read a whole bunch of reviews... They are all very similar, with not much between them. It's a tough one to call. In terms of the Nikon D40X and the D60... You're arguably better off going with the D60 based on the fact that the D60 is the upgraded replacement for the D40X. The Pentax and Sony both have internal image stabilising but then both the Nikon and Canon have lenses with IS, so that's a "zero sum" game.
Lenses are another matter. The Nikon D40x/D60 don't have a built in focusing screws. This means that you will be confined to newer lenses that have a built in motor within them. It's not a "deal breaker" though because Nikon/Sigma/Tamron are released/ing lenses that are compatible with them. So the future bodes well.
Nikon and Canon are (again) arguably producing the best (glass) lenses around in terms of quality and specifications. 3rd party manufacturers produce excellent value lenses for almost all lens mounts.
If you're looking for a good single lens that will do everything, especially since you're still new to photography. It's advisable to wait until you have a better understanding before diving in and buying a whole bunch of lenses. Possibly a 18-200mm???
You're in the right place for some great advice. So keep your eyes peeled
