Which RAM is better?

Solution
The first module has faster timing but you will hardly be able to tell a difference between the two. At this point all I would do is go over reviews and see if there are any compatibility issues with your laptop (or Mini ITX board; some use SO-DIMMs) and the memory modules you listed. If you're buying one of these modules to add with another, I would definitely consider this advice as you'll never know if two modules won't work together.

The Letter Mu

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The first module has faster timing but you will hardly be able to tell a difference between the two. At this point all I would do is go over reviews and see if there are any compatibility issues with your laptop (or Mini ITX board; some use SO-DIMMs) and the memory modules you listed. If you're buying one of these modules to add with another, I would definitely consider this advice as you'll never know if two modules won't work together.
 
Solution
If this purchase is to add dual channel or capacity to a laptop, then you must match the specs of what you already have installed. If you don't, it may not work at all. Same voltage, speed, cas numbers.
If they differ, your laptop will need to operate both sticks at the specs of the lower speed stick.