Help! Which one do I buy?

Here is the links
Arduino Duemilanove http://www.coolcomponents.co.uk/catalog/product_info.php?cPath=50_74&products_id=115
Arduino Mega http://www.coolcomponents.co.uk/catalog/product_info.php?cPath=50_74&products_id=262

Am I limited to the number of LED strips?
I need an answer so I can buy it tonight.