I don't think it matters too much. I like seats in front of the engines since it is a little quieter, but the seats to the rear are okay too.
Check with the gate when you arrive to see how many people are on the plane - if there are plenty of empties then hopefully you get one of the empty middles and you don't need to stress it.
For fuller flight, dive in to an empty row and you have a good chance that people will take the other empty spots first if they are hesitant to sit next to a young child.
Location of the changing table varies between 737-700 and 737-800, ask the flight attendant when you board if the front or rear has the changing table on your flight and maybe that's a tie breaker for which half of the plane you try for. Hopefully you can make it 1:45 without a change though.
If you do acquire an empty middle seat and your kid is sitting there, make sure to let the FA know that the child is a lap child and not to be counted as a ticketed seat when they count passengers at the end of boarding.
Home airport MDW, frequent visitor to MCO to see the mouse.
