I honestly don't see how people can't use the PS3 pads, without meaning to be patronising, but is there something wrong with your hands that you can cope with analogs being in the same place on the right side (360 compared to ps3) but for some reason your left hand is strange so can't have the same layout?
I can use both just fine and my only problem was finding the D-pad on the 360 (as I wasn't used to it) but there is one problem with the 360 layout. For people like me who adopt the 'crab' style as it's been called for some games, which you can be ready to hit any major button area (e.g. can reach D-pad, both sticks, one of the XO etc., and an L and R). Doing this on the 360 is difficult as normally on ps3 you use thumbs for sticks, and then first finger on Dpad, middle finger on shoulder buttons. The 360 would force finger on stick, thumb on Dpad which just isn't comfy at all. Meaning you have to stop to say, select a UAV on CoD whereas on PS3 you can keep on running.