While musing on the differences between Rats and Upgrade I have developed a simple system of classifying the differences between all of the types of Trashers, Gainers and Remodelers. This is not a study of the differences between plain
Trashers and
Trash for Benefit cards, but merely an attempt to classify cards based on the net add/subtract of cards to your deck.
Disclaimer: I keep editing this as new ideas come to me/are helpfully pointed out 
I propose a 6 class system; Trashers (<), Remodelers (=), Gainers (>), Upgraders (≤), Jacks (≥), Developers (±). The symbol represents the cards net effect on your deck size after you play it.
(For clarification I'm only considering the effect on the single action as you play it, not your entire turn. Also if the card offers you a choice between actions then each action requires a different classification.)Trashers (<)Playing these cards will make your deck smaller, regardless of what cards you trash or what other kingdom cards are presentI count 14 pure Trashers in the game, 15 if you count Mint's on buy effect. I won't list them, you all know what they are. But I'll talk about ones I found interesting once I classified them all.
Trading PostIt seems mad that i never really noticed before, but
Trading Post leaves you with 1 less card in your deck. This is why it is so much faster than
Mine.
Moneylender VariantsBy my strict definitions these are all Trashers, but
Moneylender, Salvager, Trade Route and
Spice Merchant all provide you with cash (and the latter three a +buy), so they do leer suggestively at better cards you can buy to replace the trashed ones and are psuedo-remodelers in my mind.
Remodelers (=)Playing these cards will neither make your deck smaller or larger, regardless of what cards you trash or what other kingdom cards are presentI only count 6 of these. Remodel, Feast, Mine, Expand, Rats and the first option on Grave Robber. I find it interesting that there are less of these than I imagined.
RatsIt was the realisation that Rats was in fact a net nuetral remodel variant that led me to create these classifications. While I understand that these are exactly the same for some reason it made a big difference in my head to think of Rats as; "remodelling any card into a Rats" instead of "trash a card, gain a Rats".
TransmuteNow some of you are waiting to point out that Transmute falls into this category, and on the most part it does, however it moves over to the ≤ category on the trashing curses loophole.
Gainers (>)Playing these cards will make your deck larger, regardless of what cards you trash or what other kingdom cards are presentI count 16 in this category, not including either Border Village or Duchess who both theoretically gain you themselves.
A very straightforward category, there's nothing particularly interesting here except the realisation that
Treasure Map is the most complex (at least in getting it to work) gainer to date.
AttacksAs a point of interest there are now also attacks with gaining benefits. Beaurocrat, Jester and Pillage.
Upgraders (≤)Playing these cards have the potential to make your deck smaller or to keep it the same size depending on what cards you trash or what other kingdom cards are presentUpgrade, Remake, Transmute and Farmland's on buy effect.
Named after the first one I thought of, Upgrade. These are more general than remodelers in that they always trash a card and have the capacity of gaining you a card but not always. For example in the absence of Poor House you can trash coppers/curses with Upgrade/Remake. This is of course a strength and not a weakness.
Jacks (≥)Playing these cards have the potential to make your deck larger or to keep it the same size depending on what cards you trash or what other kingdom cards are presentIf we needed any more evidence that JoaT was special, it turns out that until very recently he was the only card in this category. The new one is Hermit.
These two always gain you something, but optionally let you trash. Given how powerful Jack turned out to be I'm curious about Hermit now. While it doesn't have the drawing power of Jack it has a better trashing capacity and a more general gaining ability. And it can go mad.
Developers (±)Playing these cards have the potential to make your deck smaller, or larger, or to keep it the same size depending on what cards you trash or what other kingdom cards are presentForge, Develop, Trader.
The most general class of cards these ones can be net negative/positive or completely neutral depending on how you play them.
Forge doesn't really belong here because its usually used as a super-trasher and its gaining effect is a bit of a loop-hole. Trash no cards, gain a copper.
Trader doesn't really belong here either because it usually is used as a super-gainer, helping you megadose on silvers.
Develop is the only one that really sits here, and its probably why it is one of the more difficult cards to play correctly. Playing it heavily depends on what card you trash and on what cards are present in the kingdom. You might start out trashing your coppers (net negative), or remodelling your estates into silvers (net neutral), but then you start gaining and top-decking weird combinations (net positive). This provides the largest range of potential options of all
Trash for Benefit cards.
ConclusionsTo be honest I'm still thinking this over, but apart from the things I've mentioned above there is one other thing I've noticed;
while there are cards that let you trash multiple cards, and cards that let you gain multiple cards, there are no cards that do both. There isn't a trash x cards, gain x cards card for example. Edit: I was totally wrong Treasure Map and Remake are counterexamples there.
Rights, that's all I've got for the moment. Please comment on how much you love/hate this
