I think the 8753 models can be prone to LO failures but fortunately there are quite a few used spares available so it should be possible to keep one running. The CRT display can be swapped to LCD for some 8753 models as well if it gets a bit tired or fails.
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If you mainly want an HP VNA that also represents a 'piece of HP history' then the 8753 series is the classic choice. Of these, I prefer the models with the integrated test set (available with 8753D/E models) as this takes up less bench space.
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Be aware that the 8753D is a very heavy instrument, with its integrated test set and I recall that these things were a two person lift and you will need a very sturdy bench or trolley to put it on.
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The older 8753 models like the B and C will be lighter but they ideally require an external two port test set that sits below the analyser. I'm guessing the overall weight of the B/C and the external test set will be even more, but each of the two units will be easier for a single person lift.
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The later E(S) versions weigh just over 20kg even with the integrated test set. These are the most bench friendly. They generally offer the highest performance. Part of the weight saving is due to the LCD display. This display does look a bit gloomy and very dated but the ES is a very nice VNA. I used this model for many years at work.
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Due to advances in microprocessors, the processing speed (which affects sweep time) will be slower on the older 8753 models compared to the newer 8753 ones. This is most noticeable with all the internal error corrections running with a two port calibration.
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