I think you need to think about what you want out of a bar - it doesn't really matter if its carbon or alloy, or what diameter, if the bar isn't comfortable or doing what you want. Big difference between a bar designed to be stiff and direct, or compliant and comfy,.
I have always stuck will alloy as pretty much every carbon bar I have tried is too stiff for me, though I know recently there has been a shift in the market with companies like One Up producing bars that are designed to be compliant rather than super stiff and direct. I personally find a good alloy 31.8mm bar to be more "comfy" than any larger diameter 35mm bar that I have tried, irrespective of material.
From my experience the basic shape, rise, sweep etc making far more difference to comfort and control that the material of the bar, personally the rise and sweep, and the angle I set my bars at are the critical elements for a comfy cockpit.