I guess there's not a "true" answer to this question, it mainly dependes what's the stage of your startup (pre-seed, seed-funded, VC-funded).
In general, advisors get something between 0.1% - 1% of the company, vested monthly over 2 years.
The important thing here is that advisors must bring something to the table. Make that clear before engaging them, writing down what you need: a few hours per month of their time (f.i. with technical advisors or "coaches"), or introduction with X potential customers per year, or introduction with 2-3 key investors. Advisors need to be accountable, and need to deliver, as any other person in the startup.
Options- the post prior to mine (below) is correct, and the 0.1-1% number is good.