For me first comes the ECR!! Just a two lane road with no divider and no fences. Very much fun to drive in the morning. Can cover Chennai to Pondicherry(approx 130km) in less than 90 minutes if you drive in a relaxed manner but can be covered in 45 minutes itself if driven in excess of 160kmph. But very risky road to drive in the night , lots of accident cases due to drunken driving.
Next comes the Chennai-Bangalore Highway. Six lane road with median also. Very good road with less traffic except the extreme ends of the roads where city traffic builds up. Have driven only once here , my dad's Safari. Bangalore can be reached in 5 hours approx through this road. Not much of risks involved AFAIK and pretty much safe to travel.
Next comes a small stretch , a by pass route for Chennai actually. Its Maduravoyal by pass. Just a 20km stretch but can be covered in 10 minutes. Six lane road with divider and fence also. Mostly this route is meant for lorry traffic only. Risky to travel in night as the road is pitch black , no reflectors used in the lane markings , medians and road edges also. But fun to drive in the morning. Actually this is the road where i test the top speed for my Verna as it has lots of straight stretches!!