Clipless does make a huge difference in terms of efficiency and energy transfer. They also make climbing easier. That said I mountain biked with them for years and had them on my fixed bike for a year but for commuting purposes I got really sick of caring an extra pair of shoes or having to walk around in my ugly clipless shoes all day (wearing clipless shoes to the bar for the lose). I switched to clips/straps and I am happier now.

As set if you do go clipless get recesses clip mountain bike shows. I road spds but I have heard good things about eggbeaters. Half plateform/half spd are also available but then you would need to be running a brake to be safe.