Angela: I think it really depends on you. How confident do you feel pinpointing ovulation? I don't like docs/nurses that solely want to rely on OPKs for indication. Not all OPKs work for all people and in any situation, you should have back up confirmation as to impending O. Also, *most* women are supposed to ovulate 24-36 hours after trigger but as I found for myself, I don't ovulate for up to 70 hours after. So for me, triggers weren't always the best. For our three pregnancies, we used the trigger twice and didn't use it the third time so obviously knowing my body was the most important part of the equation.
Potential negatives to trigger: your egg is immature. May not be a big concern though if you're getting an ultrasound and feeling good about it.
Potential positive: trigger shots plump the lining so if you're lining isnt' ideal or is on the edge of perfect, than it could play a role. Also, triggers help to better time you for the office you're using for the IUI.If they don't work 24/7 then they would prefer to trigger you and fit you in during business hours. (this can also be seen as a negative!)
Best of luck!