If you do opt for Shimano pedals and clips, have the bike shop adjust the pedal for a loose clip in and out and perhaps as much float as is possible. As experience is gained, the pedal mechanism can be tightened. You may need to fiddle with position of the cleat, as has been mentioned earlier, to avoid knee problems. It's worth recognising that like everything else with fit on a bike, adjustment goes in small increments and over time before the optimum is found.