To/from SIN, a change at NRT has the advantage that you can upgrade the trans-Pac leg since it's on AA metal. If your flight will be after AA moves to T2, you won't have to deal with the current bus trip with its potentially time-consuming wait.

If you consider the RTW approach (which requires a minimum of 10 days from leaving North America until you return to your point of origin, to keep people on short business trips from saving money that way) check whether ORD-DEL is considered trans-Pac or trans-Atlantic. Geographically, the great circle route goes close enough to the pole for winds and such to push a given flight to either side of it. AA has treated it differently at different times since they started flying the route last year. This affects possible routings, since you have to cross each ocean once.