In the Ruby version I wouldn't use that selector with any parens. The resulting line would be one character longer than the ObjC version but use the Shift key one less time and would avoid two pinky trips out to the square brackets. (unless I am miscounting)

All other things being equal between the two options, and of course they aren't but let's just keep splitting hairs for a moment, it sounds like a typing win for the Ruby option. Readability is of course in the eye of the beholder.