alright...
all modules in the V7x modular range are top quality with every respect. as for mic pre's, V72, V72a, and the V76 and V77 versions sound great in their own right. comparisons may reveal differences, both due to difference in circuitry BUT also due to ageing. which is best depends on the app and on personal taste IMO.
V76 has 4 tube stages insted of 2 in all the other pre's. this is because of the hi/lo-cut filter, after which stages 3 & 4 serve as a buffer and o/p amp.
due to this filter, freq. response gets those little bumps in the hi and lo end just before the cutoff freq's, which some people really like and find characteristic. the filter also is available in an extra passive module called W75k. very rare, though.
with the external gain switch w77 (combined pad and NFB control, just like V76 or the SS models Vx76), you can dial in a wide variety of gains.
function (not sound-) wise the v77 provides enough gain for dynamic mic's just like the v76, but sinply without equalization.
in older consoles from the 50's, the V72 was used as an all-purpose amp - mic pre, splitter, buffer, o/p. V530 being summing amp's. later on, V76 / 77 were used as pre's, V74/74a as splitter amp's, V72 as buffer / other purpose, V75 for summing, etc...
V78 is merely a talkback amp, with limited freq response IIRC. which doesn't mean it can be modded.... but maybe limited by the different i/p xformer...