I feel the engine is the same, no difference. Many days, the engine is smoother compared to earlier versions. A major change is that the seat cushion seems excellent. You can honestly see the below compared with earlier neo.
Engine: same, no difference
Comfort: definitely good with a soft seat
Suspension: no change, but the older one was good; the new one is very firm and bouncy.
Build quality: definitely, the new one is made from the Maruti platform may be. Its build is like swift. I can see the difference between old and new. They have reduced the overall metal sheet quality; the thickness is gone..
If I get a cheaper deal for old stock Neo, I would stick to it. With older Neo, I get better, stronger sheet metal, better suspension, and, importantly, I can fix the seat with a softer cushion.