Well, these towns are not equal, a double Rampart is clearly cooler here than a single Castle.

The general principle here is this: you sort the towns by strength, for yourself and for the opponent (the sequence may differ), then you either cross off from the top of his list or from the bottom of your list. He does the same accordingly.

If both cross off competently, the result is a roughly equal pair, and exactly which one depends on the crossing-off strategy. Or you can try to catch the opponent making a mistake — if he sorted the towns by strength incorrectly.

Yes, I thought about it, it's actually logical. This way you can even end up with a pair of Necro vs Necro. If Red starts crossing off towns for himself until the end, it will be dangerous for Blue to interfere and cross off many of the opponent's towns; there's no way to catch him out — because of having a Tower himself, he risks playing a double Tower or a single town against a full double, so he must always respond to Red's actions synchronously. It only depends on him whether the Necro mirror will be played or not, and Red really risks nothing here... By the time of Blue's last cross-off, Red will have a ready setup, and if Blue crosses off his Necro in advance, Red will free up a cross-off slot by the number of towns in his pool to respond in kind. Again, if Red doesn't want to play the Necro mirror, he loses nothing by crossing off the opponent's Necro, so this move could remain in effect, I think.

Added after 8 minutes
But with this strategy, in most cases, it will be double vs double played. If Red plays by crossing off the opponent's towns, then as I showed, it will most likely be a Conflux mirror — Red is unlikely to want to play Tower against a Citadel. Or there may be variations in Blue's lineups, if in response to Blue's uncontroversial removal of the opponent's Dungeon and Castle, Red removes Conflux instead of Swamp or Rampart. But overall, these are all nuances; the number of possible non-double vs non-double lineups remains small.