Out of those options I would definitely go with the Mazda, no question about it.
Reasoning: the Suzuki, while interesting, is an orphan. It didn't sell, and it wasn't a particularly great car. Nothing wrong with it, but there are better options at any price.
The Scion was based on the Yaris, which is what I'll be using to make my comparison since I have no experience with the Xa other than my Toyota dealer neighbor telling me it wasn't a great car when it was new. The Yaris is safe, reliable, and gets good gas mileage. That is where the praise stops. It simply isn't a good car; for little more money you can get a Corolla or Vibetrix that will be better in nearly every way (I hate Corolla's, but respect them for what they are: about the perfect appliance).
The Mazda3 is a great car. It is lacking a tiny bit in reliability compared to the Toyota, and a little more in economy. But it is a much better car all around. The handling is phenominal for something in that class; the interior IMHO is much better, the leather isn't bad for fleather (fake leather; vinyl). It just feels better than a Focus or Corolla of the same time period (I have enough experience with all three that I will stand by that).
I'd throw the Suzuki out, and test drive the Scion and the Mazda and see what you will like--my nod goes to the Mazda, but I wouldn't say NO to the Scion until you've actually driven it. But the Suzuki, unfortunately, would be solidly in the no camp for me unless it is WAY cheaper. As in half the price cheaper.