havoline "formula" isn't as good as the ads say to be honest & Toyota petron isn't too bad but is not very good value for money and has less additives than other SL grade oils out there.
i only think that Zic XQ is worth using as it is a VERY advanced formula and does exactly what it says on the box. the other stuff (a, a+, etc) isn't very good value for money in my opinion.
the alto engine is quite old technology and can function fine on an SG grade oil but why not buy oil wisely and go for something which actually offer s better value for money?
many people will recall that at one time Zic was the cheapest (in price) brand and only became a hit after they signed up with suzuki, now they are the most expensive and very well recognized. the products are good, just too expensive for what they are.
sadly now they are becoming a victim of their own sucess, they are so well recognized that peopel are making fake copys of their oil and it is ruining their brand image. if you can get the real stuff and are happy with the product i don't see any reason to change brands.