The Tavern

How should melee characters beat juggernauts? They are really fast, and deal a lot of damage.

Use non-melee attacks. Throw things, shoot arrows, summon friends, evoke evokers, blast wands, do whatever it is your character does when it's not hitting dudes with weapons.

If you don't have a viable non-melee means of attack, you should probably try and get one before you do Depths next time. Spend some consumables; haste goes a long way toward winning the fight or making sure you can escape it, and pots like agility and might will take it down faster.

Or have crazy character like AC 53, EV 24 and +9 vampiric great sword.

I find that most of my actually good melee characters can melee them by Depths. Yes, they have crazy stats, but so do ettins.

Iron giants, on other hand, are a different story...

Just fight them normally. If you're really scared you can always use might, agility, or haste or use evocable summons. If you're really unable to kill them in melee, you're either playing a conjurer, for whom juggernauts are no problem, or you need to build your character better.

Is FeBe the former or the latter?

In this case I'd say he's a Summoner

With Depths' monster density Corpse Rot should be easy to deploy. Then just melee.

Curare also works!

Juggernauts are the monsters i empty my sacks of spiders and boxes of beasts on. If you're not a felid, you can even a spend a few curare needles to slow them down. Darn, ninja'd while i was testing that in wizmode.