Hi Joseluis.
The Kn 5000 I have had, and it has a very "Big" pro look about it (compared to many instruments - not just the two other ones you mention). I have played neither the VA3 - or the Yamaha 740 - so I don't know how they measure up to each other. You won't go too wrong with the kn5000 however.
The "VA" range as had a mixed reception from buyers/Potential buyers. Not easy at all to navigate say many, not so say a few!. The psr 740 is a budget keyboard, and will sound good, but wouldn't say it is has good as the kn5000 - even though I haven't heard it (save a few Demo's that is). Here In England, the KN5000 is selling for £849, the Yamaha 740 for £599.00. The Yamaha 740 started off at £999 - but soon dropped it's price after 9000's release.
The VA3,5,7 is territory i haven't yet trod, but a lot of people are saying to avoid these "VA's" if friendlyness is of your main concern.
My self? - I'd go for the KN5000! - you wouldn't regret it!. The styles are super, but so are the styles on the other two keyboards you mention. No keyboard in this Price range is going to sound terrible! (far from it) -It's just one is going to be a little better for your needs. If you use Piano sounds a lot - the kn5000 is the way to go. Strings? - well, the kn5000 is good here also - but I would guess that the new VA3 is better in this division, but may be wrong.
Jupiter5
[This message has been edited by Jupiter5 (edited 02-04-2001).]