Wizards are better than Dragons
At first, this may sound like a stupid thing to say:
Level 1 Dragons have 140 DPS, 1900 HP, and only cost 25000 elixir to train, wait what? Okay... Well, they only take up 20 housing space... Oh.
Level 1 Wizards have 50 DPS and 75 HP. They only cost 1500 elixir to train. They take up 4 housing space.
If you do the maths, the same housing space of 1 dragon, gives you 5 wizards, a total of 250 DPS and 375 hp. It's also only 7500 elixir. If you want to spend 25000 elixir, that's 16.6 wizards. We'll round it up to 17 wizards, which is 25500 elixir. It's not a big difference. We now have a total of 850 DPS, 1275 HP and 68 housing space taken up.
It may seem like 1 dragon will take a lot longer to die than even 17 wizards, but because the dragon is a single target, it actually takes less time for it to fall. 1 dragon can be attacked by all of the towers at once, whereas if you have a group of 17 wizards, most of the towers your enemy will have will be single target, unable to attack the whole group at once. They'll have to kill each wizard individually, and unlike the dragon, which can only attack one building at a time (usually), the group of 17 wizards can attack up to 17 different buildings at a time. On top of this, the use of wizards makes air defense, air bombs and flying skeletons completely useless as a defense method. They can also take out a Barbarian king in a few seconds.
In the end, a horde of wizards will fell many more towers and clan castle troops in its lifetime than one dragon, and it can be deployed in multiple places at once. You can spread a group out easily, which negates the mortar. If they're suitably spread out, the wizards will be causing the maximum possible destruction to the base that they can, and each mortar will only be attacking one or two at a time. If you combine them with a hero, that hero can even destroy some of the walls, or maybe set off the traps, before the wizards are deployed, leaving the base wide open.
I'm aware there are plenty of overpowered strategies with dragons as well, but the fact of the matter is, I've strategically used both wizards and dragons, and I've won with wizards far more times.