If you're looking for pure dps rogue is the way to go. In an ideal situation they will do more dps than a similarly geared monk.
Raids in this game, however, are rarely ideal. Its not always possible to be behind a mob. The goal of any melee performing a dps role is to be behind a mob (in order to avoid mob dodges parries and ripostes) but a monk will be able to do a respectable amount of dps in a much wider arc.
Point being both monks and rogues do great melee dps. It really comes down to play style. So here's a little comparison. I didn't play a rogue at all until late Kunark so I don't know as much about them in classic.
Monk Skills:
Feign Death: Best pulling tool in the game, saves your butt a lot, not so amazing till lvl 30 or so.
Mend: Amazing, once you get over 101 skill you have a free 25% heal every few minutes. It never fails after 101.
Defensive Skills: Monk defense allows us to tank a mob with little trouble. However monk defense is all avoidance and little mitigation. When you get hit you get hit very hard. Twinked out you should never have a problem tanking a mob in a group, but may have trouble holding aggro.
Weight Limit: This part sucks. Monks take a hit to AC the more you are over a certain weight limit. This hit can get brutal at times. /split helps a lot. Learn to love it when grouped.
Fist Progression: Your fists get better as you level. Every 5 levels you get a damage increase. At level 25 your delay starts to go down as well. Monk fists start at 4/36 and are 14/30 @ lvl 50. If you're twinking use 2 Enameled Black Maces until lvl 30/35.
Soloing: You can solo as a monk. Mend + bind wound allows you to solo better than rogues.
Flying Kick: Looks awesome, doesn't do as much damage as backstab but no angle restriction.
Rogue Skills:
Sneak/Hide: Explore explore explore! Great for CR, great for getting to that ass/supp group in lguk when bats are up.
Backstab: Owns, huge numbers.
Illusion masks: WTB the pre-nerf guise my monk on live had
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Poisons: I hear they're bugged here so I don't know... they were nice on live.
Soloing: Don't try it without a Rubi BP imo.
Defensive Skills: Rogues are the glass cannons of the melee world.
Kick: Spell interruption is good!
Honestly someone with a rogue main would be better qualified to talk about the class than myself. I'm partial to monks, but my main was a monk for nearly 5 years.