I too had swift (2014 model 46k driven) before switching to alto vxr (2019) and I also own a wagon r that is 2018 model 31k driven. I have observed the following:
Engine power
We cant compare alto and wagon r to swift in this domain as pkdm swift comes with 84 HP engine while wagon r and alto comes with 67bhp and 48 bhp respectively. Swift has abit better power to weight ratio as well compared to wagon r. Coming to alto vs wagon r, honestly I havent noticed much difference in acceleration of both cars. Reason could be the better power to weight ratio of pkdm alto. As I have manual version of alto, I never found it underpowered with 5 ppl on board with ac on.
Fuel economy
Swift never gave me more than 10kmpl with ac on no matter what I did. However, it might have given better average had I tried 0w20 oil in it. I only had chance of single oil change on my swift and I poured 5w40. Wagon r too was not giving more than 12 kmpl with ac on but ever since I switched to 0w20 oil, the fuel economy of wagon r has improved slightly. Alto definitely takes lead in this department. Even with my heavy foot driving, alto doesnt give less than 16-17 kmpl with AC. With moderate foot driving, it easily gives 20-22 kmpl.
AC performance
I have observed that both alto and wagon r has superior ac performance compared to what my swift had to offer. Maybe its AC needed servicing but by default (in the condition I received the car), its AC struggled. Coming to alto vs wagon r, on a hot summer day with equal sun exposure to both cars, alto`s ac has slightly better cooling compared to wagon r however latter has better fan throw since cabin filter is not provided in wagon r by default.
Build quality
Interior build quality wise alto and wagon r are almost same, a bit superior to swift. Exterior build quality wise wagon r and swift are way better than alto.
