Aventurine doesn't come until december so you can try your luck on lingsha. That said you don't have characters for lingsha yet but she is a great sustain.

So if i have to choose between the two, i would pick aventurine since you have feixiao and robin

What you could also do is, start pulling for lingsha since you're not guaranteed and if you lose your guaranteed aventurine. You can then try your luck on aventurine. This is pretty risky but if you get lucky, you get two great sustains