If what you want is to refill your potions as quickly as possible, playing either Potion Motion or Skull Riders is probably the fastest way.  If the latter, be very aggressive, especially trying to snipe mobs as they spawn, and you can both kill and die fast, doing enough of the former before the latter to refill a potion.  Choo Choo Zoo and Sorcery Stones can easily take half an hour or more for one game.

Note that when it gives rewards after a game, there are four spots, each of which can be bronze, silver, or gold.  The higher your score, the more spots have something, and the better quality of the item in the last spot.  The first slot is mana refill (or potion, if your mana is full), and very easy to fill up in most games, except for Dueling Diego, where KingsIsle messed up and made the threshold too high (as noted in the article).  The second slot is gold, and reasonably easy to fill up in most games.

The last two slots are for low level items or treasure cards.  The items are low level no matter how well you score and regardless of your own level.  Getting an item in the third slot is doable in most of the games, but it does take a decent run.  Getting something in the fourth slot is very hard.  You basically have to either get on the high score list or come pretty close to it.  Getting #4 on a high score list got me a silver quality item in the last slot, and #2 a gold quality item.

My guess is that potion motion is dominated by macros that make moves at random really, really fast.  There aren't that many possible moves, so it's possible to make a considerable fraction of them pretty quickly.  It's hard enough to catch which ones work that random moves are often useful if you don't see one that is obviously valid.

Conjuration is almost certainly dominated by screen capture software.  It's much easier to make matches if you have the various cards at the start on the screen next to the game in front of you, copied from when it shows you everything at the start.

Are those two items cheating?  Perhaps.  But if you're going for a high score, you're almost surely competing against others who do take that approach, which is really a flaw in the games themselves.  The other games strike me as less vulnerable to that sort of hacks.