I would compare the Mazda 3 GX (sedan) to the Kia Forte (sedan) but I find the Koup is the way to go when it comes to the Forte.
I see a lot of the posts here have been about looks. For me, that has a certain weight but I honestly like the looks of both cars.
I know guys that have had the 3 for years and never did anything on them except oil changes. Stories vary from owner to owner. I think both cars are solid. The 3 does drive extremely nicely though. Now that I've test driven it again, I honestly feel jealous when I see one because I know how much fun it is to drive.
I've not driven the Kia for a few months so am looking to test drive both cars on the same night hopefully.
Kia Koup advantages: looks, features (heated seats, bluetooth etc), warranty.
Kia Koup disadvantages: shifting, clutch, steering feel, poor resale value, creaks, and the dreaded crease issue.
Mazda 3 GX advantages: driving dynamics, handling and steering feel, smooth shifting/clutch, 4 doors
Mazda 3 GX disadvantages: warranty, possible rust problem (should be fixed, but who knows....)
Pricing is not really an issue since both would come out to almost the same price (with Kia having the edge in features though). The difference in price is there if you want to add things like heated seats/mirrors, fog lamps to the Mazda 3. But those are not necessities for me.
Will re-evaluate after my next test drive. I am also test driving the Ford Focus soon.
BTW I've read and posted on other forums like the Elantra forum. People in general tend to be quite objective even if they own the car. The Elantra is still in the game too but I'm slowly losing interest in it due to the choppy ride. Otherwise it seems like quite a good car for the money. They are having no problems selling those.