Both the Atlantic and the Pacific can be rough. After all they're both big oceans.
The frequency of rough weather depends of course on the season and where you are doing the crossing. From now on and until next spring the low pressures are linig up between UK and the states, while further south (south of the canary islands) there are stable easterly winds (the passat) all the way over to the caribbean. This route is very popular among sailing boats crossing the atlantic.
Today weather forecasts are quite accurate many days ahead so cruise ships have more alternatives when it comes to route planning, but as a main rule the winter season is more rough than the summer