AES-Serpent is probably not less safe than AES; it's just not necessarily as much more safe as you'd expect.
A much bigger concern than which precise ciphers you're using is which block cipher mode you're operating under; Truecrypt/Veracrypt uses XTS --- like most disk encryption --- which (among other things) isn't authenticated.
The funniest thing about TC/VC's cascades is that the keys are derived from passwords anyways: a giant clunking complicated block cipher cascade resting on top of a low-entry password secret. It's just a silly design.
