I think this issue has been covered many times over the years.
2 sticks is better than 4 sticks.
Pros of 2 Sticks
1. Overclock easier
2. More stable
3. Less Power usage
Cons of 2 Sticks
1. More expensive
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Pros of 4 Sticks
1. I guess I can be cheaper in some ways
2. I looks nicer because your board is filled up
Cons of 4 Sticks
1. Can't overclock as well
2. Chances of a stick going bad goes up
3. Some motherboards lower the speed if it sees 4 sticks