I have both the C5 and SW127. Each of them has their own merits.
They are different in optical construction with performance in my opinion being about the same.
The SW127 would be slightly better in observing the planets whereas the C5 is a bit more portable.
The C5 is a Schmidt Cassegrain, focal length 1250 mm at f/10, weighing about 6 lb.
The SW127 is a Maksutov Cassegrain, focal length 1500 mm at f/12, weighing about 8.5 lb.
You can use Google to see the difference in construction between the two.
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Celestron C5 vs Skywatcher SW127
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