If I want to go through Naga City with as little effort as possible, I grab the Human Paladin and prepare a Dragon Shield + The Glowing Guardian. The Paladin's natural resists along with the Dragon Shield gives him great physical resists from the start, and along with the Glowing Guardian's prayer beads, he gets a reasonable amount of magic resists. Combine that with the Human's significant damage boost at higher levels, Halpmeh (which is much more useful when you have higher resits), and the extra level you get thanks to Humility (you're going to hit 10 either way), you can wipe the floor with most bosses. Humility + Absolution is also great for easier leveling topside. It's also an excellent combination to do the dungeon Feeling Parched (GG is great for that in general, just convert all your potions for piety)"
The most powerful run I've had through the dungeon was certainly the Monk that Lujo just described... I prepped the dragon shield + Binlor and, after grabbing Stone Form and Stone Fist, spammed as much Stone Wall/Stone Heart as I could while still getting to the Arena with lots of piety to spare. Requires familiarity and skill with the Monk, a class which I used to avoid, but amazing to pull off.
My second win in the dungeon was a Human Asassin prepping Tikki Tooki. Tricky (though maybe it's 'cause I wasn't as good back then, can't remember much of that run). I kept trying to make the Goblin Asassin work, and then realised that the limited stuff I could take down was seriously hampering the usefulness of my Racial trait.
Generic Tips for Naga City, in case you didn't know/hadn't thought of those:
-Prep a burn salve or buy one in the dungeon; you'll want to desecrate The Earthmother at some point
-It's a good idea to remember the boss lineup, figure out which boss(ess) represent the most trouble, and have a plan for them (Frank is usually one of them
-Enter the Arena a bit short of leveling up (I usually do it right before level 8), so that you can either heal up right after the first boss or mid-fight depending on your first three opponents
-I wouldn't hesitate too much with using potions and other resources on the first boss or two if you need them, since you're at a lower level at first and so the power difference between your character and the boss is more significant... it's a lot easier to regen-fight lvl 10s as a lvl 10 hero, so long as you've properly leveraged god abilities both upside and in the arena. Just make sure to preserve a good portion of resources for your more challenging matchups (And Kinnissssch, depending on your character!), keeping in mind the prices of the altars and stores of the Arena.
-I feel like Humans are generally one of the best races for this dungeon, since their bonus really scales best in late game (levels 7-10), which is where you take on the most important part of the dungeon.
Some of these might be obvious to you or the vets, but it took me a while to get a feel for them
Once I got those ideas down well, Naga City became a lot more approachable.