Help Understand Low-level Roulette

[Velox]

There are a lot of factors that go into the DF's party set-up AI. There is actually a hierarchy system which you can use to your advantage to get faster queues.

The first thing it does is look at your role, which is given top priority. If a certain role (DPS, Healer, Tank) is needed in one place more than another, the DF automatically tries to pump those roles into their most-needed locations.
Next the DF looks at each role breakdown. As you know, the DF will try to optimize part compositions as much as possible given the players queued. For example, the DF tries to put together the following jobs for a full party set-up.

1 PLD
1 WAR
1 WHM
1 SCH
2 Melee DPS
2 Ranged DPS

In order to optimize party composition further, it will try to make sure there are no duplicates of any class/job so that the Limit Break gauge isn't hindered. This doesn't affect tanks or healers currently since there are only 2 of each, but for DPS it can create a difference in queue times quite drastically. For instance, the number of ROG/NIN currently using the DF will be higher than normal given that it was just released. There are more than enough ROG/NIN to have them fill all the DPS slots, but the DF doesn't WANT this outcome. After one of the many ROG/NIN are chosen, the DF will then attempt to find 1 Melee DPS that's either a MNK or DRG, and 2 Ranged DPS that are either BRD, SMN, BLM. Now if the DF fails to create the ideal party composition, only then does it start doubling up on classes/jobs. However, because there is an over-abundance of ROG/NIN currently floating around, their position in the party hierarchy is at the lowest in the eyes of the DF. This means that, assuming everything else equal, a MNK or DRG will have a shorter queue time than a NIN, and that BRD, BLM, and SMN would have shorter queue times than any melee DPS. Of course not everything is equal because more players prefer some classes over others (there are a ton more BRDs than most other jobs which skews queue times a bit as well for all jobs).

I'm not going to go into every detail because there are a LOT of factors for the DF's decision-making process. It's not necessarily level 50's getting priority, it could very well be timing. A MNK or DRG would naturally have a much shorter queue than a NIN right now, regardless that they were level 50.

According to friends/family + personal experience, here's a listing of all jobs rated according to general queue times (lower numbers having shortest wait). Most of these were judged during peak hours (4-9pm PST) so things may vary if you play late night or early morning. Things will change as people cap NIN and stop queuing with it as well.
1. WAR/PLD (almost instant for each, difference is negligible)
3. SCH
4. WHM
5. MNK
6. SMN
7. DRG
8. BLM
9. NIN
10. BRD

[whiskeybravo]

According to friends/family + personal experience, here's a listing of all jobs rated according to general queue times (lower numbers having shortest wait). Most of these were judged during peak hours (4-9pm PST) so things may vary if you play late night or early morning. Things will change as people cap NIN and stop queuing with it as well.
1. WAR/PLD (almost instant for each, difference is negligible)
3. SCH
4. WHM
5. MNK
6. SMN
7. DRG
8. BLM
9. NIN
10. BRD

I almost always get 5-6 mins q's on DRG and MNK.. BRD, SMN, BLM (in my experience) take the longest to q for a dungeon/trial (like 11-16 mins avg). Nice explanation btw

[Velox]

I almost always get 5-6 mins q's on DRG and MNK.. BRD, SMN, BLM (in my experience) take the longest to q for a dungeon/trial (like 11-16 mins avg). Nice explanation btw

This is true. Like I said, theoretically ranged DPS classes should have shorter wait times, but what messes this up is that there are a LOT more people playing ranged DPS than melee DPS overall. Much of this is attributed to ease-of-play. Ranged DPS classes tend to be easier to play than melee (SMN is an exception) due to not having as complex rotations or positional requirements. They are also the safer classes to play, allowing for more mobility and less risk of dying to enemy-centered AoEs (there are a lot of enemies that cast AoEs around them). Before NIN was released, a HUGE portion of the playerbase was playing BLM and BRD, giving them the longest queue times. Once the level of NIN players starts dropping it will return to that trend until 3.0 mixes things up with all the new classes/jobs they will be adding.