I am also trying hard to choose between these two programs (for a different grade level.)
I ordered the first few Light Units of CLE, and just the student handbook of GWG so I could get a 'feel' for both programs.
Here's what stands out to me:
GWG is mostly just fill in the blank exercises and diagramming. CLE mixes things up a bit with crossword puzzles/word searches, etc - so it is a bit less 'boring' than GWG.
I don't care for the spelling portion of CLE as much, though. The list appear to be based on 'themes ( EX. - camping, flashlight, lantern, etc.)
We are used to phonics/rules based spelling, and so I am a bit worried that CLE spelling would confuse my son.
I like that GWG has less lessons per year ( you would only need to do grammar 3-4 days per week vs. CLE where you would need to do grammar 5 days per week to finish all 10 light units in a regular school year.)
CLE is more 'portable'. You got your grammar, spelling and penmanship in one handly little workbook if you need to go somewhere. (We often have doctor/therapy appts during the day for my younger DD.)
With GWG we would have the bulkier workbook, plus the student manual, PLUS separate spelling and penmanship books. A full backpack!