In my years of instructing I found that it's much harder for a student to go from glass to 6 pack. I'm a proponent of starting in a 6 pack. It will keep you focused at the learning at hand rather than getting distracted by all the built ins you'll find in a glass cockpit. Also it aids in building a solid mental moving map of what's going on (especially during instrument training). Having sound situational awareness is an important part of flying if not THE most important during instrument flight. The glass cockpit can easily become a crutch when it comes to those important skills.