Other than new cards, I'm not sure those choices really need to be mutually exclusive.
But I chose new levels, by which I mean new types of levels instead of just more birds and more snakes (which, I suppose, is cheating and sneaking a second poll answer in of new enemies to go with the new levels).
There have been a lot of avian and serpent levels over the past year, which gives us a color pallette of a hundred or so brown levels in a row (with the exception of the 50 blue/green serpent tower levels). Some additional map variety would be appreciated, in terms of visual appearance, strategy required, enemies faced, etc. Maybe an underwater area where we battle aquatic enemies, or a forest area, or anything but more brown maps where I just drop slow/poison and sit back and wait.
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New Cards: I did not choose this because I've been playing for a long time and have a fairly strong battle deck already. Unless they're legendary-quality cards, no new card is going to replace a high-level Tesla or Volcano Tower, for example. Other than a "gotta catch 'em all!" mentality, there's no real benefit to adding new cards that are weaker than ones I've been building up for thet past year+. Unless, of course, they add necessary functionality for a new area (e.g., Illuminator Tower and Flare for the serpent levels)
New Game Modes: While this would probably be my second choice of the available options, I did not choose this because I'd rather have new content than find reasons to replay the same existing levels ad nauseam. The new Challenges feature is great, but I don't need more reasons to keep replaying the same content over and over unless the rewards are better than I anticipate.
