Hmmm...
Both are equally good, although sometimes megs is a notch ahead of mothers.
I have used megs ultimate polish and I can safely say it is one of the best ones in the market. Super easy application and removal and the result is a wet, glossy finish.
I haven't used any mothers prodyct excely except for their carnauba shampoo and it is definitely good stuff.
Go for what your heart tells you. I would go for meguiars. 
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