I have not testdrive the Swift, but as the owner of Tiida, I think Swift's driving position encourages sporty feeling (without sacrificing space). And for 649,000THB you get all the safety equipments while in Tiida you'll have to shed 100,000THB more unless you're ok with the Latio.
If you're usually travel with only one passenger, then I think you should go testdrive Swift first, then try Tiida.
("I just edit the price you wrote na krub Mr.CHENG" : J!MMY)