Conflux: I agree completely. Magic Elemental, by itself, is comparable to the weakest level 7s like Bone/Ghost Dragons. In fact, even unit for unit comparison undervalues the town. 1 big difference is, for other towns, you can say, oh, Black Dragons are very powerful, but the rest of the army is not particularly gold-effective. You can pick out a unit that can compares to a conflux unit, but he won't have the rest of the overpowered army to fight with in his town.The best town in terms of raw firepower is Conflux (because they neglected to balance it) followed by Castle. Both have high costs, so it would be slightly harder to build them up, but Tower is the only town that would be severely crippled by having a small map or a high difficulty.
Stronghold and Fortress both have fast and somewhat inexpensive tech trees (high cost in wood and ore though) that might be better on small maps, but Hydras are junk and Behemoths are only good because you can get them in the first week with little difficulty. They also can only reach Lvl3 Mage Guilds, but Fortress at least has the best native terrain type (swamp)
The worst town is probably inferno, because it only has two really standout units (Hell Hounds and Efreet), and all the others are sub-par in comparison, not to mention the relative expensiveness for what you get.
Everything else is somewhere in the middle, but Necropolis has an obvious advantage on large maps because that means there are more skeletons to raise.
Sprite + Air elemental, and you got a shooter + no retaliation flyer for clean sweeps, and fastest on the map for a lvl 1+2 army. Add Ice Elemental and you sacrifice some speed for fire power.
Energy Elemental + Mind Elemental + Phoenix and you got a 3-stack-fire-immune armageddon army, etc, etc.
Castle: While archangels are awesome, half of the castle army - not quite as much. The whole town is well balanced and most units do their main job well (which is more than some other towns offer), and the stables is an excellent privilege to add to that, but they are nowhere near "overpowered" like conflux.
And most of us do think Inferno is the worst. Not by much. And if you play in a map where you are guaranteed to find a few more Inferno towns spread around the map, the teleport facility might even bump the town back to average.
I think most of us agree the rest are more or less average. I personally prefer the ones with some spectacular units, Black Dragons, Harpy Hags, Titans, Vampire Lords, Hydras, Mighty Gorgons, etc.
I disagree a little with the Necropolis. While you can grow a huge number of skeletons in a huge map, skeletons are also very slow and that will not help that much in a huge map where ground speed is more important. Generally Necroplois needs time to build just like the tower. They are very different so they are a lot of fun. But A LOT of units (zombies, wight/wraiths, bone/ghost dragons, pre-upgrade vampires, preupgrade lich) are just so weak the whole army is barely average, and a good deal below average if caught before it is built up.