The PST tanks are quite popular for that reason (although new).
The bottom line is that PST tanks - or any steel tank - is negative throughout the dive. While this sounds great, AL80's are a better choice for some because of the fact that they pass through neutral as they empty... In other words, they're never too light and never too heavy. For much of the dive, in fact, they're nearly neutral. Steels are always negative.
...Which is good if that's what you need. However, many find that having "all that weight" that far away from their body does bad things for their trim. I've found that when diving wet, they will "turtle" me, or make me prone to flipping over on my back. This is because they make my center of gravity further back than my center of buoyancy.
I'm afraid I don't remember whether or not I posted this link already, but if I didn't... Here it is:
http://www.bftwave.net/lcscuba/homebc.html . There, I touch a little on the concept of proper trim and avoiding a center of gravity and a center of buoyancy that's too far apart, creating an "opinionated" BC.
The key is to find out not only how much weight you need, but also where, exactly, you want it on your body. Done properly, this can be achieved using any type of BC, although with a bp/wing it seems easier due to the weight of the metal plate.
...So the bottom line is, "How much weight do you need," and, "Where does it have to be on your body to achieve proper trim?" Additionally, there are two other things to consider: If you rent tanks regularly, what sort of tanks are available to you? You may want to stick to AL80's simply because they're so available... You know, so that when you travel, getting the "right" tanks is easy. Lastly... And perhaps most importantly... Is this: If you're fully weighted with a full tank (i.e. at the beginning of the dive) then can you swim your rig up in case you have a bladder failure? I mean, if you can't inflate your wing/BC at all, can you still swim the whole shebang up? If not, then you'll need to ensure that you can ditch enough weight to be able to do so... Which is something that you can't do if the weight is all in your tank.
...And it's because of all of these variables that we haven't been able to answer your questions directly... Like, "Which tank should I get?" It completely depends on the situation. If the tank you select meets all of the above criteria, then I'd say it's a good purchase.
