PPS for preferreds is irrelevant. The lower the better. Just find the ones that pay the biggest divis, that have a
$ liquidation value attached. No matter what happens to Ford and GM , their preferreds are in great shape. Keep your eye on GMS and HGM and try to find the bottom. Great divis and discounted prices. Even if GM folds and creditors and preferreds are only paid out at 50% upon liquidation ( which is not going to happen), they would already be a good buy. If they don't fold and liquidate, you already know what the benefits are.
Good luck, and as Warren Buffet says, " Be fearful when others are greedy, and be greedy when others are fearful."