So, I was thinking about what the most overrated PrC is, and I think I've got an answer. Of course, I'm sure many will disagree... after all, it wouldn't be overrated if people didn't think highly of it. But my vote? Frenzied Berserker.
I mean think about it. What does this class give you? It gives a bunch of melee damage over 10 levels, but forces your party to find ways to control you when you go berserk and opens the possibility of killing your own. And the damage it gives? Really not that much compared to what you could have had. Consider the class FB build:
Orc Fighter 4/Lion Totem Barbarian 2/Frenzied Berserker 10. Power Attack, Cleave, Intimidating Rage, Destructive Rage, Improved Bull Rush, Shock Trooper, Leap Attack, Headlong Rush, and EWP: Spiked Chain or Meteor Hammer. Make your weapon valorous. Okay, so you get 6:1 returns on Power Attack, +10 Strength from Frenzy, and an extra attack while Frenzied. With a Valorous Weapon and Headlong Rush, you're doing triple charge damage, so at level 16 you're looking at 288 damage per hit from Power Attack, +21 damage from the extra strength, and you've got 5 attacks. All this whenever you charge. Very nice. If your strength when Raging (but before Frenzy) at this level was 35 (which is pretty reasonable) and your weapon was +5 (easy enough), you're looking at 5 attacks for around 400 damage per hit. Very impressive, and it will likely one hit kill any enemy... or party member.
But now let's look at the exact same build, and just drop Frenzied Berserker from the equation. We don't need Cleave, Intimidating Rage, or Destructive Rage anymore (but we'll keep two of them anyway). Also, we can switch over to Whirling Frenzy, which doesn't work with Frenzy but does work on its own. Also, I believe an errata or FAQ stated that you can't Frenzy while mounted, but we're not Frenzied now... so we'll drop Leap Attack and go with a mounted option. So now we'll go with Zhentarium Fighter 10/Whirling Frenzy Lion Totem Barbarian 6. Nice and simple. For feats, we've got Power Attack, Improved Bull Rush, Shock Trooper, Headlong Rush, Mounted Combat, Ride By Attack, Spirited Charge, Extra Rage, Intimidating Rage, Imperious Command, Cleave, and Great Cleave. Whatever, I was running low on ideas for feats at the end there. With a Valorous Lance, Spirited Charge, and Headlong Rush we now do quintuple damage on the charge. Our strength goes down due to the loss of Frenzy, but we still have the extra attack (since Whirling Frenzy is in play). Our Power Attack returns drop to just 2:1 due to the loss of Leap Attack and Supreme Power Attack, but we've got that tasty multiplier. So now we've got 32 damage from power attack, +18 damage from strength, +5 damage from our weapon, and an extra 1d8 damage from the Lance itself, for just 59.5 damage on average... but then multiply that by 5 to just under 300 damage. It's not as much as the Frenzied Berserker, but here's the main point: it's still enough to kill easily. And now we're not screwing our party over if we go berserk at the wrong time, plus we can swift action anyone to cowering if we want and we had plenty of feats to play with.
So how can the FB be such an amazing overpowered class if we can still do the same job with just the base classes involved? Especially since we don't get the rediculous drawback of "you might slaughter your whole party?"
Now, I'm not saying it's a horrible class by any stretch. But for most overrated? I think it's a winner.
The other option is Radiant Servant of Pelor. Yeah, you don't lose anything but a few hitpoints, and that's fine, and it's a solid choice... but what you gain is the ability to use in combat cures a little better. Since when have in combat cures been something worth cheering about? By the time your ability to cast really awesome cures comes around, you've already got Heal.
JaronK