12AU7/12AU7A

The only difference between the 12AU7 and the 12AU7A is the "A" version can be used in series string filament circuits due to it's controlled warm-up   cathode.  Otherwise, there is no difference.

6189/5814

Both of these are "milspec" versions of the 12AU7.  They may also be marked with 12AU7WA.  They both have thick mica wafers which give the tube extra rigidity which minimizes any microphonic problems.  Their cathodes have been specially designed so they can withstand many on/off cycles and long periods in cut-off without any degradation of performance.  The 5814 has a slightly higher filament current demand than the 6189/12AU7.  Some (not all) Sylvania Gold Brand versions of these tubes have gold plated pins. 

5963

This tube makes a decent substitute for the 12AU7 as the characteristics are almost the same.  The 5963 has a slightly lower plate voltage rating compared to regular 12AU7.  The 5963 has a max plate voltage of 250V while 12AU7 has a max of 330V. This tube has a specially designed cathode which can withstand long periods of time in cut-off without hurting the tube.

7730

This is a premium version of the 12AU7 made only by CBS/Hytron.  This tube has very low noise characteristics and heavily plated gold pins.  These were intended for critical test instrument applications, but due to their superior low noise performance, these make excellent choices for audio applications.

6680

This is the mobile communications version of the 12AU7 which can withstand +/- 20 % variations in filament voltages without any degradation of tube performance.

ECC802/ECC802S

These are "premium" 12AU7's which were marketed by European manufacturers.  I don't think that there was any difference in manufacturing technique, to create these, rather they are just specially tested 12AU7's that exhibit very low noise/microphonics and matched sections.

7316

This is an Amperex tube that was a premium grade 12AU7