I agree that South Sudbury is far more accessible (Routes 20, 126, 495, Mass. Pike).
I did a commute of Marlborough to Cambridge for a few years. I found that if I couldn't flex my hours around the commute that route 20 to 126 north to route 2 was the best way. If I could flex my hours around the peak times then I would cut down to the pike via 85 and then route 9.
The pike is much faster but not during heavy commuting hours.
What part of Sudbury?