enum values: NSInteger or int?

There is now NS_ENUM starting Xcode 4.5:

typedef NS_ENUM(NSUInteger, NSCellType) {
    NSNullCellType = 0,
    NSTextCellType = 1,
    NSImageCellType = 2
};

And you can consider NS_OPTIONS if you work with binary flags:

typedef NS_OPTIONS(NSUInteger, MyCellFlag) {
    MyTextCellFlag = 1 << 0,
    MyImageCellFlag = 1 << 1,
};