It seems that many car reviews say more about the personal preferences of the author than they do about the objective merits of the car. As a result, there are plenty of conflicting opinions. In the case of the Spider, some critics prefer the suspension tuning saying that it gives more confidence - the exact opposite of what Jalopnik concludes. All critics that I have read seem to agree that the Spider has a more comfortable ride, but disagree substantially on whether or not they prefer the handling characteristics. Several have indicated that the Miata has more body roll in the curves, which some like and others don't, and that the Miata is much more lively and challenging, which makes it more exciting and engaging. Others prefer the solid feel and confidence of the Spider. Some like the mid-range torque of the Spider, while others prefer the linearity of the Miata. I don't think this makes one better than the other, just very different, which is a good thing. What would be the point of two identical cars? For me, the smoother ride of the Fiat and reduced body roll make it more pleasant to drive since I often have my wife sitting in the passenger seat with me. We live in the flat desert and the fun curvy mountain roads are an hour or more away, so for me, having a roadster that is enjoyable to drive on the highway with less noise, better passing power, and a smoother ride are all significant pluses. I have a friend who owned a Miata for a while, but sold it because his wife wouldn't ride in it. The Miata is going to be a better choice for some and the Fiat a better choice for others depending on what they like and how they're planning to use it. It's great that they're not the same. If they were, I probably wouldn't own a roadster at all right now. For me, the Spider is unquestionably the better choice.
I like this Miata/Spider comparison review by Jason Cammisa of Motor Trend because he drives and compares them back to back, both on the road and on the track.
I find it interesting that he really believed the Miata was faster because it felt "so much faster," but in reality the Spider's lap was .01 seconds faster than the Miata. I can understand where some people could prefer the spirited feel of the Miata to the more controlled feel of the Spider. But personally, I think the ability of the Spider to go fast without having to work so hard at it and feeling like you're pushing every limit is a positive.