See WANT, first of all I will let you know.

Then, put it this way IR1 prcess is in three steps: 1) Service Center 2) NVC (national visa center) and 3) embassy
I applied to CSC in 2006, since I am a USC now my I-130 is out of processing time and they should take care of it soon. Process in NVC used to take about 4-5 months but now with new precedure it takes some where from 1 - 1.5 month.
embassy in each country is different and the interview time is variable. From two weeks to 2 months. I know this guy on VisaJourney and he had the same situation and he is finished in 3 months.
Advantages: your spouse enteres with GC. Social security comes in two or three weeks (usually) and they have work authorization (comes with GC) and it is cheaper to do it this way.
K3 is almost equal timeing but with current situation lots of dis-advantages.
One more reason I won't apply K3 is I applied in Feb. 2006. Now some applicants have reported USCIS mis-understood their application as soon as K3 came in and they got probably a new date so their case is not our of the processing time anymore and doesn't get much of the attention for 4-5 months in the serivce center.
This subject is debatable for ever but I hope this way that I am taking right now will work just fine for me.
I will keep you all posted with experience here so you can make a better disicion on your case.
Peace