In no particular order: Efficiency, sound levels, CFMs, fan speeds, dehumidification rate, operation temperature range, build quality, warranty, aesthetics, plus all the bells and whistles the higher end models have like RF remote, wifi capability, occupancy mode, temperature sensing from remote, horizontal and vertical louvers swing, programmable swing, programmable operation, auto cut-off, etc.etc.
Now different people value different things so it's up to you to determine what you want and what you don't want to pay for.
One thing is for sure, the high end systems are fit and forget kinda things. We install them and as long as the owner performs the minimal required maintenance, we dont get called back for trouble, and the units last.
And if something was to happen, the 10 year warranty assures the customer peace of mind.