For the month of May, South Point's great promo is back. $25 worth of points can be exchanged for a $50 Chevron gas or a $50 Wal Mart card. The best game available is NSUD (99.73%) in .25 through $2 denominations. The limit for any one player's account is ten cards; you can mix and match.
It's relatively easy to learn decent NSUD. Even if you ignore penalty cards, you can still get up to about 99.65%. That's still +EV, given that the value of the gas cards is 0.6%. The bottom line is that you can get $500 worth of gift cards for an expected loss of about half that. If you don't want to bother, then there are plenty of 9/6 JOB machines available at 99.54% with perfect play, which is very easy to achieve.
Furthermore, that level of action should get you future consideration in the form of room offers. South Point is kind of wackadoodle in how and when they send mailers/offers, so I've found that the best approach is to call a casino host and refer to past play. That might be a good way to score some free/cheap rooms this fall.
I would generally lean toward Wally Mart because Chevron is usually the most expensive gas in town. But it's a real no-brainer, now that one of my local Wallys has a gas station!