http://www.ffxiah.com/item-sets/205523

1st option:
This set has 30% Dual Wield (40% with /NIN), 24% Haste.

2nd option:
Full AF3+2 with Twilight Belt would have 25% Dual Wield (35% with /NIN), 24% Haste.

3 AF3+2 pieces vs. 5 AF3+2 pieces. Since it hasn't been measured enough to determine the exact proc rate, we'll just go with 5% difference between those two (although current testing suggests it to be even lower). So assuming 5% with 3/5, 10% with 5/5.

Now with option 1, we would have (1-0.4)*(1-0.24) = 45.6% delay. Option 2 would be at (1-0.35)*(1-0.24) = 49.4% delay. Meaning, in 100 attacks option 1 would get 8 extra attacks in.

Assuming a 5% set activation rate for option 1, that would mean 35%*5% = 1.75% activation rate. Set 2 on the other hand would have 3.5% activation rate. When the effect activates, the second and third hit are tripled, offhand swing is swallowed, although I won't count that for now. That means a ~133% damage increase per activation (100% if you count the missing offhand swing).

So to compare..

1st option:
108 hits with 1.75% activation rate, so would activate on 1.89 hits, meaning..
Hits = (108-1.89) + (1.89*2.33) = 108 + 1.89*2.33 = 110.5

2nd option:
100 hits with 3.5% activation rate, so would activate on 3.5 hits, meaning..
Hits = (100-3.5) + (3.5*2.33) = 100 + 3.5*1.33 = 104.7

Which means in the same time, option 1 would give 5.5% more hits. Now remember, this is without consideration for the missing offhand hit, for the fact that it's quite probably a far lower activation rate than suggested here and for any kind of other Haste you get from spells or Haste Samba, which would make the difference in Dual Wield even stronger. Daggers don't matter for this, since all of these effects are applied to the number of hits, so it will scale to whichever weapon you use.