you can remap the car just fine bro, in stock form that is, Monster Sport ECU if you refer to that might be different ballgame. On the other hand stock ECU tune does 175 hp stage 1 (which is 10 hp more than MS ECU with that airintake and exhaust?)
They are actually very different cars in different categories. But if i had to choose, i’d go swift sport for the fun factor ( turbo engine , tight and nimble chassis and of course the 6 speed manual ) . The 1.5 mazda 3 is definitely underpowered for its size but if you really need the extra space then you’re better off with the mazda.