I've used both, and found the Somas more secure/rigid, but that's not because of the clips. It's because I was using laminated leather straps versus thin, synthetic leather straps on the All-Cities.

Get whatever clips you can afford, and invest more time and effort in finding good straps. In the end I find cheap plastic clips to be just as good as steel, as long as you've got quality leather to hold your foot in. The clip is just there to keep your foot from sliding forward and to keep the straps from flattening down on themselves.

Even the aforementioned BMX pedal + fat velcro straps combo works well, despite completely doing away with the clip.