If you are looking for the best subs in the San Fernando Valley, try Big Mo's Subs (across the street from DeVry University, between the city of Chatsworth and the Fallbrook Mall-- sorry I forgot the exact streets, I know the place by sight). Fresh ingredients, fresh bread, family run business. I've been eating there for two decades, and the subs still taste great. Try the hot roast beef sub or the Philadelphia, if you want something spicier.
On a side note, I also wish more of these threads specified what part of LA they were talking about. I'm interested in food in the SF Valley, because I won't get on the freeway unless I'm being paid to do so.