The best way I have found to use the 'new member' $100 rebate, is to
try to get as many player points on your card as you can, limiting
your losses to NO MORE than the $100 rebate amount. If you win a lot
during your session early, play conservative the rest of the way to
protect your winnings. If you are only up a little or down a little
with 20 or 30 minutes left, crank up your denomination and play hard
till the end (again losing no more than the $100 rebate).
while that's the way to go if you value player points highly, it also
subjects your $100 to as much churn as possible, with the house taking
3-8% on each play since you can only play slots, not vp.
i prefer the polar opposite approach - head over to vip slots, stick
your $100 in a high-denomination slot, and hit spin. if you win big,
celebrate. if you lose, head straight back to the players club and get
your $100 back. (you don't have to wait an hour.) this minimizes churn
and hence maximizes expected return.
side benefit: it will be perhaps the only time in your life when
playing a slot machine for $100/spin is actually rational. be sure to
maximize the drama! bring friends. be drunk. scream a lot if you hit
anything, pissing off the grumpy high rollers who are in the vip area
to avoid people like you. 
As far as what to do with your $100 freeplay, players generally use
their own personal preferences on how to play it.
you have to play it through one time. for that one time, pick whatever
game best maximizes combined ev and fun factor for you. after that,
it's cash. do whatever you'd do with cash in a casino. play it, spend
it, whatever.
cheers,
five