My understanding is that all preferred shares are treated equally. So they all should receive the same percentage of face value in a liquidation. However the price varies quite a bit from series to series even taking into account that some have a face of $25 and some are $50.
My suspicion is that there are some hoping that the suspended dividends for preferred shares might someday be given out by a court decision - so the ones with more accumulated unpaid dividends may be worth more. The theory is that the net worth sweep is a dividend on the senior preferred - and based on the wording of the preferred shares they get their dividends as long as the company gives out any dividend to any class of stock.
My recommendation as to which preferred to buy - I think getting unpaid dividends is very unlikely, so I just buy the cheapest ones. Maybe I'm missing some important detail? Also be careful that some of these are very lightly traded with a huge difference between bid and ask, so never, never do a market order!
Also - my understanding is that until the preferred shares are paid at 100% the common shares get zero in a liquidation. The "preference" is complete, not a percentage.