Despite the obvious personality difference they are somewhat similar. Here's what I can remember in terms of differences.
Len:
Cats, faster movement, smooth ice spears, turns into a cat when crouching. uhh... anything I missed?
W-Len:
Illusion dash, chargable 236a, multifaceted ice spears, 214a/b/c
And I think their fake outs have different commands.