If you can't accept the risk of riding a motorcycle with no helmet, you shouldn't ride with one. Helmets increase your chances of surviving a head injury by about 30%, which is a lot, and why I would always wear one, helmet law or not...but...you are 30 times more likely to die riding a motorcycle than driving a car. Helmets reduce that risk to 23 times, or something like that. The best way to improve your odds isn't wearing gear, it isn't spending $1000 on a helmet, it's making decisions to reduce risk, including the decision to not ride if you don't feel safe.
So: the difference between a DOT helmet and a Snell helmet is really going to be measured in a few percent worth of safer-ness. It's not really worth debating, if you ask me. You should get the best gear you can, that's a no-brainer, but I think we're arguing angels on the head of a pin.
That said, traditionally, the Snell standard was geared towards higher-speed impacts that a racer might encounter. DOT is more for street speeds. Typically, street crashes are less than 30 mph. The Snell 2010 is more DOT-ish, so the differences are very technical, and I'm sure a Snell-approved helmet is every bit as safe as a DOT, but saying one is better than the other for all kinds of forseeable impacts would require a convoluted and overly technical a argument and I don't think it's true at all.
Bottom line? Snell means it's a well-made helmet, as Snell does check out their approved helmets. DOT helmets don't get inspected much, it's more an honor system kind of deal (and there are plenty of dishonorable companies with failed helmets. Check if your model has passed:
http://www.helmetcheck.org/default.aspx), but I feel good about wearing DOT-approved lids. Just because a shorty lid can get a DOT sticker doesn't mean it's a bad standard--that's like saying half a loaf of bread can't be edible.
Buy a well-made full-face motorcycle helmet from a reputable manufacturer that fits you properly and don't worry about it any more.