I've seen people say Mongoose it better due to higher that, and then seen people argue that DS has far higher proc rate therefor overall better.
What are your thoughts?
You have a couple different issues here:
1. Dancing steel has a 2.3 RPPM per weapon, which means that each one will proc it 2.3 times per minute pretty much guaranteed. The proc will give you 62 str/agi for 12 seconds,
2. Mongoose has a variable proc chance per weapon attack, which means that the slower the weapon, the more times it will proc. 1.9 speed weapon will give it 3.8% chance to proc on each hit, while a 2.6 speed weapon will give it a 5.2% chance to proc on each hit. The proc will give you 90 agi and 22 haste for 15 seconds.
Overall, Dancing Steel benefits from the RPPM system by increasing the proc chance every hit in combat where it doesn't proc, which is affected by haste. This increased chance is capped by 10 seconds and resets if no attacks happen after 10 seconds passes.
Mongoose, on the other hand, can proc back to back, it can proc more often than 2.3 times per minute, or it can proc less. The fact that it's random means that there's a chance you see it more often than Dancing Steel, but that chance is not guaranteed. Good luck can favor you, proccing it back to back often, or it can frustrate you, proccing hardly at all over the course of several fights.
However, the amount of the proc (90 agi), combined with the attack speed increase (22 haste), as well as the longer duration (15 sec), gives Mongoose some advantages, especially for classes that really benefit from haste and ToT.
For a rogue, if you're choosing between DS and Mongoose, I would suggest Mongoose, since you hit so hard already, a proc pretty much means you're going to obliterate people.
For a monk, I'm not sure, since their viability is always affected by not having healing buttons or strong teammates. I'd like to think Mongoose is better, simply because of the higher benefit, but more up time might make DS better.
For a feral druid, I'd rather just use 25 agi enchant, since you only have one weapon and that decreases the proc rate of any enchant by half.
Other enchants to consider: Executioner (90 crit rating on proc), Elemental Force (104-120 dmg on proc), Colossus (absorb shield on proc), and Windsong (56 haste or crit on proc).
There may be other enchants to think about too, but I don't feel like going in depth here about them all.