I have the Ignis Sport which has the M15A 1500cc engine, the Swift Sport has M16A 1600cc engine, I believe that the 1.3 is a M13A engine so all common family.
I will be upgrading to Swift Sport when I rack up the miles on my Iggy as I have been totally taken by it, and though have only sat in Sport it feels and looks great. I know someone with a white Swift 1.3 and she absolutely loves it and has had no issues with it whatsoever.
Jug has made some very interesting points about badge perception etc when Suzuki put the design brief together for the Swift it was to be as good if not better than what Europe and to offer, I think it succeeded in that.
Although Swift is new, the Ignis came third in reliability table from JD Power last year in supermini cat, and with the Swift being a newer car with developments of same engine I see no reason why it should be any different. Plus Suzuki I think were ranked 7th best dealer's in UK as well.
I know that from this months EVO mag they are working a Supercharged Swift with short ratio gearbox to capitalise on the success of the Junior WRC campaign that they have been running now for a few years starting with the Ignis and working through to the Swift.