This is the stuff of which long war threads are made, generating lots of heat and somewhat less light - unless you specify which areas of the market we are talking about - and remember that TLD selection is a 'horses for courses' business.
It should be fun though, and out of courtesy to the original poster I'll play by the rules set in the OP - so here it goes (with lots and lots of assumptions I simply have to make about time frame, business type, purpose, etc and which I would be happy to discuss later):
1. .COM (w.w.a.b.k.)
2. -
3. -
4. .org
5. .us / .de / .co.uk / .eu
6. .net
This is guaranteed to be controversial, I know, and apologies in advance to any big .net holders here - I also have .nets and sure hope something will be done soon to enable this venerable extension to find a purpose again.
Just my $0.02