I just though I'd start a list of assignments that people have found to have good bang for the investment. I'm doing these from memory right now.
If you have more, just add them below and I'll update the top post
Trade EC for commodities or commodities for EC
Time: 30 min
Trade XP: 5(?)
DOffs: 1 | Telepathic, Unscrupulous, Trader are good
If you've got someone with unscrupulous, or telepathic, just do them when you have the EC or commodities on hand. If you don't have the commodities on hand, I'd say its not worth replicating them for the mission. You'll lose out on EC.
Time: 3 hours
Military XP: 43 (?)
DOffs; Any 2 (including colonists)
Commodities: 50 provisions, 50 medical supplies, 15 shield generators
Pretty nice military exp for a 3 hour mission. It only takes 2 officers, and you can actually sent colonists to complete this. Shield gens can be bought cheap at ESD, Provisions at Andoria, and Medical supplies on Vulcan. Also, 0% failure from assigning 2 common Colonists.
Send a Representative to a security briefing
Time: 1 day
Military XP: 186 (?)
DOff: 1 security officer
Good bang for your buck and only takes 1 DOff if you've got the security to spare
Medical: Send medical relief to X
Time: 1 day
Medical XP: 349
DOff: 1 medical, 1 science | Medical and science traits boost success chance
Commodities: 30 Medical Supplies
These are by far the best assignments I've found so far for bang for your buck. Bucket loads of medical XP and with a medical and science officer, you're looking at a 21% chance of critical success and a very low failure rate (though I've yet to get a crit success, but I do have 5 cooking today, so we'll see tomorrow if I get one).
Colonial: Resettle colonist
Colonial XP: ?
I don't remember the requirements for these assignments, but these are worthwhile because they net you 5 common colonists. So far I've seen 3 different colonists, 1 Vulcan, and 2 humans. Colonists are good for colonial assignments and military resupply missions. Awesome for filling a DOff slots for missions that don't have Trait modifiers.
Science: Investigate Temporal anomaly
Time: 3 hours
Science XP: ?
DOff: 1 security, 2 any officer | telepathic boosts success chance.
Why do this one, has a default 3/47/47/3 success/fail rate but if you do succeed, you get a Very Rare DOff!
Time: 1 to 3 days
More DOffs, what else is there to say? Crit success with net you 3 DOffs from the Department specific Cadres (Tac, Eng, Sci) which take 3 days. The plain Junior Officer Cadre is 1 day and nets you 5 common DOffs of random category.
Recruitment from the Civil Corp
Time: 3 days
More DOffs. I've got one cooking right now, so I'll update you on what you get out of this, but I assume you'll get Bartenders, Entertainers, Diplomats, Advisors etc from this.