This is one of those "it depends" situations. One main piece of information not mentioned in your post is what value you put on your company and what value you put on your consultants time. Another thing that you don’t mention is whether or not the consultant will also be paid in addition to receiving equity.
Which is more preferred 20 percent in your company or one percent in Google? Get your numbers in order and the answer really boils down to simple math.
Personally, I pay for as many services as I can with stock to preserve my cash; so long as I maintain controlling interest there is nothing preventing me from diluting shareholders.
Also, as Jsaunders stated, if you do provide this consultant with equity make sure you agree upon a vesting schedule.
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A thinker sees his own actions as experiments and questions--as attempts to find out something. Success and failure are for him answers above all.
Friedrich Nietzsche