Is Rich or Abundant better?

In The Old Republic, many of the crew skills are moderate, and it's fairly obvious that Rich and Abundant are both better than moderate, but is Rich yields the best? Or Abundant? Are there other possible qualities of missions?

Bonus: Does quality of the yields increase the difficulty? That is to say are my crew more likely to succeed if I do a moderate yield mission?

As I recall, the progression is Moderate → Abundant → Bountiful → Rich → Prosperous → Wealthy – although the latter two require mission schematics to unlock.

As to the second part of your question, yes, the difficulty increases. Check the color of the yield; if it's orange there is a chance your crewmember will come back unsuccessful. Gray, green and yellow are almost automatic success, although you will not get a crewskill increase from gray missions and only about half the time from a green one.

EDIT Here's a quick breakdown on the difficulty:

• ORANGE: Highest chance of failure; guaranteed +1 to skill, possible +2 if successful.

• YELLOW: Some chance of failure; guaranteed +1 to skill

• GREEN: Little chance of failure, only occasionally increases skill

• GREY: Virtually no chance of failure, never increases skill.

Rich rewards more than abundant.

Consider the two missions, both of which reward Grade 1 Biological Samples:

Tirsan Spice - Abundant Yield

Boma Breeding - Rich Yield

The abundant yield mission costs 120 credits, and the rich yield mission costs 295. Additionally, the abundant mission requires 15 skill, while the rich yield requires 55 skill.

From this, we can logically conclude that if Rich didn't reward more (on average) than Abundant, there would be no reason to ever perform it, as it would be more spent for less gain.

(Alternatively, I have my own anecdotal evidence than Rich > Abundant, but I figured the numbers are better evidence)

As to your second question, the results of the mission are irrelevant - what matters is your skill in the trade skill compared to the minimum required skill level. The greater the magnitude of the difference, the lower the chance for failure. This is represented by color, with "Orange" meaning "most likely to fail" (but also guaranteed to skill up!) down the color spectrum to "Yellow", "Green", and finally "Gray", which is (I believe) a guaranteed success (but gives no chance to skill up).