While there is often debate on the virtues of high-level and low-level campaigns, I think it’s more interesting to talk about the “sweet spot” is in terms of levels. That is, what’s the level range for the best gaming experience? Obviously it’s a subjective topic, but I think the rules can point us to a likely set of numbers.
Looking at magic-users, I think the definition of the sweet spot is driven by the spells that are available at different levels. When you think about the “classic” spells that are the most iconic, you think of spells like lightning bolt, fireball, hold person, etc. Those 3rd level spells are where the magic-user class really comes into its own, and they start to become available to 5th level magic-users. Thus, I put the bottom of the sweet spot for magic-users at 5th.
Looking at the top of the range, I look at 5th level spells like cone of cold, teleport, and the last of the wall spells. Once you get past those, there are spells that are undeniably more powerful, but simply not as iconic as those we see in the 5th level spell list. And 5th level spells are available to 9th level magic-users.
From a magic-user perspective, I’d thus put the sweet spot at 5th-9th level. Illusionists lag behind ever so slightly, not getting 5th level spells until they hit 10th level, but I think that can be regarded as an outlier.
I think that range works for clerics, too. That’s when we get the more useful clerical spells such as dispel magic, animate dead, create food & water, etc. It also takes us through the last of the cure spells (significantly, I think) and raise dead. I think the spell lists argue for the cleric sweet spot to also be 5th-9th experience level.
In that same 5th-9th experience level zone, druids get their ability to change form, paladins have their warhorse, rangers start to get their spells, and thieves for the first time have a better than even chance to hide in shadows. Monks, ever oddballs when it comes to the other classes, does the thing that’s iconic for them in this same range; they start having to fight to advance in level once they hit 8th level.
In terms of the iconic spells and powers of the various character classes, we see a real comfort zone between the 5th and 9th levels of experience. That’s when they start to get all the cool powers they were expecting, yet before the range where the nature of the game changes. It’s also, undoubtedly not coincidentally, the range in which most classes hit “named level”; 9th level high priests, 9th level lords, 9th level paladins, 9th level wizards, and 9th level thieves. Some of the sub-classes buck the trend slightly (10th level illusionists, for instance) but these are only minor changes.
For me, the “sweet spot” in AD&D is 5th through 9th level. What about you?