I think the quality is about the same. Like TwoWalks, I am not a fan of the Pietta base pin, but that is easily replaced with an Uberti pin if desired. As of a few years ago, the case colors on the Cimarron Model P is much darker than a standard Uberti Cattleman. To me the Pietta Frontier frames and Model P frames look very similar, with the Pietta having perhaps a tiny bit more color. The Model P has several details that are more authentic than the Frontier, but the Frontier has a lighter action out of the box. Some of that is the lighter main spring, which is hour-glassed somewhat. Whether they are also polishing more inside I'm not sure. I think the nice actions on the Pietta is due to Alchemista (Alessandro Pietta) being a cowboy shooter and knowing what cowboy shooters want. The heavier springs in the Uberti are more like a real Colt.
I like the Model P better myself but that is for the small details. As for cost, in the most recent price list (Jan. 1, 2014) the Pietta is only a few dollars less than the Uberti.