Closed. 
Hello, welcome to the forum.
Data sheet on both say 10 or 80 samples/second. How do you plan to get 100?
"Two data rates are supported: 10SPS (with both 50Hz and 60Hz rejection) and 80SPS."
That said, an Uno has the same processing power as the Mega, you only appear to need a few IO connections.
So it boils down to how big your program will be and how much SRAM it will use - do you plan to have really big arrays for the relatively slowly sampled data?
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