The biggest difference I'm seeing between Len and White Len is that it seems easier in general to land hits with Len, but easier to perform combos and get more damage in with White Len once you've connected. I always wanted to play Len, but she seemed too awkward and terrible to be worth it compared to my other characters (lol Warachia), but I find White Len to be more fun and combo-friendly (mostly thanks to 623a being the best move ever for saving sloppy/awkward combos).
I do like Len's facial expression and color swaps better though, but White Len seems more fun and her combos are more aesthetically pleasing.
Also a Len/White Len tag battle team is one of the most awesome yet horribly confusing things ever.