Q. Is Swift is safer than i20?

Any car is safe or unsafe depends on your driving skills and road manners & attentiveness while you drive. people get killed in the most strongest SUVs like fortuner or range rover. If you mean to ask about build quality, yes Swift is less weight compared to to i20. If you want a battle tank which doesn't drive well & drinks petrol or a perfect drivability with lot of fun and great mileage...you decide.

To add, don't think heavier car are safer. in 2015 scorpio got a 0 star rating in crash test. So a lighter Swift with ABS and airbags can be safer than a i20 without them

Well, that only a crash test can confirm which is better but better go with the version which had ABS and airbags