The GPS functionality of the G1000 and the G430/530 is very similar, but while the 430/530 only has one knob and a few buttons for input, the G1000 has a keypad and softkeys. Makes a big difference in how you control the unit but at the end of the day the units work the same way, with a little added functionality for the G1000.
I am not familiar with the Chelton but do they now have their own standalone GPS units?
What was the bad experience with the Garmin 530s?