The list of possible iOS resource suffixes sorted by their priority on different devices.

gistfile1.md

iPhone 5: -568h > ~iphone > @2x > .

-568h@2x~iphone
-568h~iphone
-568h@2x
-568h
@2x~iphone
~iphone
@2x
.

iPhone 4/4S: ~iphone > @2x > .

@2x~iphone
~iphone
@2x
.

iPhone 3GS: ~iphone > . > @2x

~iphone
@2x~iphone
.
@2x

iPad 3/4: ~ipad > @2x > .

@2x~ipad
~ipad
@2x
.

iPad 2/mini: ~iphone > . > @2x

~ipad
@2x~ipad
.
@2x

gistfile2.m

- (NSArray *)suffixesForThisDevice {
    NSMutableArray *suffixes = [[NSMutableArray alloc] init];
    
    NSArray *heights = ( UIDevice.iPhone && UIScreen.tall ? @[@"-568h",@""] : @[@""] );
    NSArray *idioms = ( UIDevice.iPhone ? @[@"~iphone",@""] : @[@"~ipad",@""] );
    NSArray *scales = ( UIScreen.retina ? @[@"@2x",@""] : @[@"",@"@2x"] );
    
    for (NSString *height in heights) {
        for (NSString *idiom in idioms) {
            for (NSString *scale in scales) {
                NSString *suffix = [NSString stringWithFormat:@"%@%@%@", height, scale, idiom];
                [suffixes addObject:suffix];
            }
        }
    }
    
    return suffixes;
}