I promise you if wis/dex quarterstaff healer cleric/monks were so heart-stoppingly op they'd be the standard cleric people run instead of the 23/4/3 scimitar one. But, hey, I got fifteen minutes.
@Lorkas: You're forgetting improved expertise, which all strength clerics these days run.
@perek586:
They don't get more AC, and they don't get overheal, and they don't get the quarterstaff monk APR, nor free imp knockdown. WisAC+DexAC heavily outweighs shield+full plate, not even counting the APR gained from going QStaff.
It's a direct downgrade going anything else
Battlecleric stats to beat, from memory (23/4/3 build). For the sake of argument I'm doing travel/plant on both, since imp invis isn't 'really' ac.
Both Clerics 'Base' AC: 10 base+6 tumble+10 magic vestement+5 shield of faith+5 barkskin+1 dodge+4 haste=
41.
Battlecleric adds 11 armor+1 dex for 53, and due to having some spare feats grabs improved expertise (they all do this, if they know what they're doing/using easily available forum builds) for a total of 63 with the lights on. I'm sure there's something I'm forgetting, but whatever, the numbers are for direct comparison anyway.
Cleric/Monk (I'm assuming 24/6 due to comments about free IKD and the fact that any less than 23 cleric levels is absolute madness for this sort of thing) adds 9 maxed out dex and 15 maxed out wis, for a total of +24 with the lights running. That is, a final AC of 65.
Huh. That looks fine, except for one problem.
http://nwn.wikia.com/wiki/Flat-foot
You don't have uncanny dodge. So, unless you're dueling one opponent, cut that final AC by 9, for 56. Roughly two points ahead of a non-IE strength cleric. Note: This assumes you never modify your 14+2 gift dex, which, you shouldn't, because you lack uncanny dodge.
So, a tie, with battlecleric losing when out of IE, and winning against more than one target.
So, AB Fight:
Both get: Divine power ('20' BaB, I guess) +5 epic, 5 divine favor, 2 battletide, 3 Mdamask weapon, 3 epic weapon focus: 38
Battlecleric: 7 str mod+6 buff mod: 51 AB. APR of: 51/46/41/51/51
Cleric/Monk: 3 dex+6 buff, -2 dual wield: 45. APR of (should be) 45/43/41/39/37/45/45 (main hand) 45/43 (off hand). You can get to 10 APR if you hit flurry but that's another -2 drop. Mileage.
So, AB is worse but you get more attacks.
Damage:
Both get etc. Comes to, like, +20 or something. Lets pretend it's 20, I'm getting kind of bored. Essences, spells, etc. This isnt the right number but it's round.
Battlecleric adds: 6 epic weapon spec, 7 str mod, 6 buff mod, 3.5 scim average- 42.5 at a higher AB, generally. Crits on a 16 for 85.
Cleric/Monk adds: 4 (divine power strength)+3.5 (main hand average or 4.5 offhand average), for a total of 27.5 or 28.5. Crits on a 19 for 57.
So, battlecleric does more damage raw. With five attacks, assuming all hit, 1 crit (25% chance, give or take?), damage ooooof.. 255. Assuming all of a cleric/monks hit (this is being extremely kind, however) 277.
Difference is, then, relatively negligible minus two thorny problems: all of your attacks aren't going to hit, meaning the higher AB str-cleric will come out with more damage, one- and the low base damage of the cleric/monk is more prone to get outright ignored due to DR, immunities, etc. Death by a thousand cuts has never worked super well here.
Other stuff, ie, the elephant: A human gets eight feats. For a cleric/monk finesse quarterstaffer, you lose 4 of those feats getting dual wield running. 6 monk gets you IKD (at, like, level 29.....), so lets pretend that means you only 'lose' 2 feats. But you still need, to be 'competitive' to a battlecleric in melee: blind fight, weapon focus, improved critical. This leaves you with one selectable feat pre-epic. The battlecleric needs not lose 4 feats off top, and gains another 2 from pre-epic fighter levels to boot. So, it wins on feats.
A battlecleric, as well, should only lose 2ish AC when flatfooted (1 dex, 1 dodge), vs 10 (9 dex, 1 dodge) give or take on the monk.
And, finally: Choices and restrictions. No uncanny dodge, no umd, way less skill points, and a stricter stat spread, on the Cleric/Monk. You could take fighter and shore up your incredibly lacking feats- at the expense of 3-4 more lost cleric levels, making a dispel-bait character option even worse (battleclerics can shore this up with abjuration defense because they've got extra feats), or you take rogue, get umd (I can't, at this point, play chars without umd) and uncanny dodge, and your skill points and have the same 'dispel bait' problem.
Also, the str cleric is going to have more discipline and raw AB so if it's an IKD fight between the two, welllll. Getting knocked over is the same as being flatfooted, innit?
DISCLAIMER: I didn't account for spell focuses on the cleric/monk, because you Need every spare point of wis you can get, so almost all epic feats that weren't otherwise dedicated (epic focus, etc) were spent maxing out that wisdom score. If you want spell focuses, epic spells, etc, you're going to see your AC drop a few points, ruining that anti-armor edge. I also didn't account for the battlecleric's 2d6 sneak attack, which would've flipped the damage gap: 290 on the battlecleric.
tl;dr: Cleric/Monk can get better AC when not flat-footed, and can deal more damage against low AC targets, but the battlecleric deals more raw damage at higher AB, is less starved for feat and skill options. Pound for pound I'd take the battlecleric over the cleric/monk any day, because I consider UMD and a hefty heal score better, frankly, than anything the healer path can muster. Also, the battlecleric has more feat and weapon flexibility. (You could however skip the q-staff on the cleric/monk, max out at 8 APR, and gain 2 AB and 3 feats! It's not uncanny dodge but it's something.) Also, the str-cleric is more 'battle ready' prebuffed, if that matters to you. It'll have an easier time leveling, too.
tl;dr2: So, really, it depends on what you like. They're fairly even barring my, erh, personal preferences. Of course, there's not a category for 'getting called cheesy on the forum for having monk levels on a wis-caster class,' but know that the battlecleric wins that fight every single time.
But for a stealth cleric I wouldn't recommend the monk/cleric unless you Really don't care about any of the above! You'd need higher int for hide/ms, rogue levels, etc! A dex-y cleric/rogue/fighter with a large shield on the offhand might work? You'll have a rough time, though, as above.
