Factor: I'll rather use words, instead - for a scale one would probably need clearer defined reference points... Of course, the verbal description also reflects my listening experience over more than just these two headphones, but it seems more appropriate, nevertheless...
Let's see...
DT531 / K240S
-resolution/detail: ok (somewhat recessed in the midrange, though) / quite fine
-soundstage: medium (quite nice) / small (fairly intimate, though - and squishy, when not driven well)
-bass response: good (fairly extended and punchy) / fine (probably on the border to overdone for some, though... and either too fat or recessed, when not driven well)
-efficiency: ok (amp recommended, but also works fairly well with integrated amps et cetera)/ ok (low impedance output amp strongly recommended - doesn't need too much juice, though)
-comfort: fine (light & plush) / fine (featherlight, but not really good for hot environments due to the pleather pads)
-isolation: poor (maybe 2 dB or so...) / poor (maybe 3 dB or so...)
-durability: Dunno - fairly resistant to that heavy smoking & cable rolling of mine, though. Otherwise I don't really stress my headphones very much, though, so I really can't tell...
Greetings from Hannover!
Manfred / lini