Living in Chennai, I just took a long ride in both the new buses (Tata Marcopolo & AL Viking) without any real work and just for the sake of posting a review

. And my view is given below. This is totally my opinion and there are obviously some differences to mine and other's views (like refinement at idle of Marcopolo & windshield wiper design of Marcopolo). Also, it's just a review from end-user's point of view and not from an experts point of view.
Exterior Design:
The Tata Marcopolo is built in a spanking new facility in Karnataka while the Viking series has been built by many coach builders like Prakash, Veera, Irizar-TVS and the like with Ashok Leyland providing them the bare chassis and the design factors. Seeing them on atleast a couple of dozens of instances everyday, Tata Marcopolo stands out with the most modern design of the two. When viewed head-on, the Viking tends to pose some threat to the Marcopolo with it's modern multifocal headlamps lending a touch of class and modernness to an otherwise traditional design. The Marcopolo is also quite a looker with it's Volvo-inspired headlamp design. Where the Tata trounces the Viking is in the safety aspect with it's two huge wiper blades covering the entire windshield compared to the paltry single blade in the Viking, hardly enough to cover the driver's side of the huge windshield. The story from the rear is a sloppy one-sided affair with the Viking coming with a decade-old but trustworthy design. The Marcopolo exudes a level of modernness and follows the same design theme like the front with circular-themed tailights, plastic shrouds for the lights and body-colored plastic bumpers.
Interiors:
The Marcopolo scores in the interior design department as well with well-appointed, spacious seats and good level of standard features, the most notable among them being the "Emergency Stop" button in each of the vertical rods that supports standing passengers. The ergonomics around the driver's seat is also impeccable with everything falling nicely to hand and easy to operate. The only noticeable grudge is the lever for holding the windows open, which is very old-school and could have been easily replaced with something much better. The Viking though comes in a tried and tested, less-modern, interior design that does not disappoint both the drivers and the common public. The only grouse is the uneven height of the seats directly above the rear wheels thus reducing the space available for the passengers in the next seats. There is a lost of weight reduction in the Marcopolo with Tata preferring plastic over sheet-metal in many places. Though it serves as a great advantage in the mileage aspect, the long-term reliability of those parts are still unknown.
The Ride:
From what I experienced, the Viking seems to have a better pick-up both when starting from a standstill and while climbing inclines, though this may also be completely because of the driving skills of the respective drivers involved. But, I have noticed it on more than a couple of occasions. Also, the Viking's engine seems to burn fuel and combust more efficiently than the Marcopolo as it does not spew smoke out of it's exhausts like Marcopolos do. I have seen old Marcopolos emitting a plume of black smoke in Delhi and Bangalore but I was shocked to see barely weeks-old new Marcopolos doing the same in Chennai. It definitely needs to be given a thought by Tata. The Viking also seems to have better riding comfort as it sails over road undulations with minimum fuss unlike the Marcopolo which strains itself in situations like this, with it's modern frame and construction designed for truly modern roads. The Marcopolo, though is extremely refined and vibration-free unlike the Viking. Particularly impressive was it's refinement at idle, to such an extent that it was difficult for passengers at the rear to make out whether the engine was switched on or not.
Verdict:
As such, the Tata Marcopolo seems to have just edged out the Viking in the initial race going by the feedback of the general public, but only time will tell whether the new Tata will hold it's own against the rock-solid reliability that has endeared the Ashok Leyland Vikings to the traveling public. On a last note, the drivers I spoke to seem to prefer the older and traditional Vikings to the Marcopolos. As they say, it takes time to change perceptions.
I have also posted this with photos in my blog
ANYTHING ON WHEELS.