Hi there!

Do you have any historical data from previous visitors?

1366 might be a little large for the average laptop user, 1024 may seem a little more appropriate.

I know there are users here who strictly design under 1000 wide.

We use 960px as our default, but sometimes do as wide as 1200px in specific cases where more width is needed.

A good idea is to check your GA to see what screen resolution most of your visitors have.

940 or 960 seem to be most common.

The 960 grid system was pretty popular back in the day, so many designers seem to stick to it out of habit.

Personally, I like to use 940px for some reason. Works well on a number of different screen sizes.