Can anyone give me the low down between these 2 classes. Since I haven't played a ninja yet I was wondering what everyones opinions were. I am going for my 3rd or 4th party and don't really feel like playing a ninja to level 10 or so just to see how he does.

i play with both now but neither is high enough level for me to really say which is the whomper.
looking at their skills tho:
ninja gets thrown-based penetration and thrown-based crits

monk gets crits, damage reduction, and martial arts bonus

just from this it would seem a ninja would better lend itself to thrown weapons and the monk should be a melee character

be able to tell ya more in a few lvls i hope

Don't forget that ninja also get the critical strike skill bonus meaning they will instant kill more often. They are also a good sub for a rogue type class wth lockpicking and pickpockets. I have a High level ninja and she can really dish it out with her bare hands. and she is lethal with throwing because she auto penetrates and has a chance for an instant kill with them. So putting a ninja in front with a thrown weapon or two in the alternate set can be a lethal combination. The one complant I have with the ninja is the high EXP cost to gain a level.

As for a monk the only one I have played is RFS-81 and he is not an accurate example for obvious reasons.

Hope this helps.

I have both a monk and a ninja in front lines (along with fighter) and a ranger in mid line with my 2 spell casters. This way I get 3 guys with critical hit potential (monk,ninja,ranger) the fighter for beserking damage. All my guys can do ranged attacks as alternate weapon. The major difference bewtween monk and ninja are as follows from what I can see at 12th level.

Monk (dwarf) = Martial Arts Bonus
= Damage Reduction (right now its 18% and I think
it applies to physical damage only)
= Critical Hit
= Psionic Spells
= Effective when Blinded

Ninja (human) = Thrown Weapon Bonus
= Critical Hit and Thrown Critical Hit
= Rogue Abilities of Lock Pick/Traps/Pick Pocket
= Alchemist Spells

In terms of effectiveness in combat both do about the same for damage and attacks per turn with punches and kicks. They tend to critical about the same as well. In ranged combat ninja fairs a bit better than Monk. For Spells I tend to build up their fighting first but any magic school can be good regardless of type. The Ninja has rogue skills while Monk has damage resistance. Thats the main area to look at, if you have no one to handle locks, traps, pick pocketing then go for the Ninja. If you want a good fighter type Monk is a good choice since they can take a pounding especially when certain abilities approach 100 and unlock special ones.
Or you can do what I did go for both and enjoy all the pluses.

:D