I
t's a no-brainer to believe in free will. There are plenty of ways to go about it, but the punnet square of choice is probably the simplest.
Free will either exists or it doesn't, and you can either believe in it or not. Obviously, if free will exists, it is better to believe in it. But if free will does not exist, then I cannot make a choice about whether I believe in it or not, since I have no free will.
If you believe in free will and you're wrong, you were always fated to be wrong, and it's not your fault; no one can blame you for your error. If you don't believe in free will, and you are incorrect, you may in fact be to blame, and you ought to exercise your free will and change your ways to conform with reality.
"Believing in free will" dominates "not believing in free will". To the best of your ability, you should strive to believe in free will and act accordingly, technically regardless of the evidence one way or the other; since you have nothing to lose by being wrong. That said, there is extremely good evidence for free will, and very good moral reasons to believe in it besides.