Only using class names is not sufficient in your case.
By.cssSelector(".ban") has 15 matching nodes
By.cssSelector(".hot") has 11 matching nodes
By.cssSelector(".ban.hot") has 5 matching nodes
Therefore you need more restrictions to narrow it down. Options 1 and 2 below are available for CSS selector, 1 might be the one that suits your needs best.
Option 1: Using list items' index (CssSelector or XPath)
Limitations
Example:
driver.FindElement(By.CssSelector("#rightbar > .menu > li:nth-of-type(3) > h5"));
driver.FindElement(By.XPath("//*[@id='rightbar']/ul/li[3]/h5"));
Option 2: Using Selenium's FindElements, then index them. (CssSelector or XPath)
Limitations
Example:
// note that By.CssSelector(".ban.hot") and //*[contains(@class, 'ban hot')] are different, but doesn't matter in your case
IList<IWebElement> hotBanners = driver.FindElements(By.CssSelector(".ban.hot"));
IWebElement banUsStates = hotBanners[3];
Option 3: Using text (XPath only)
Limitations
Example:
driver.FindElement(By.XPath("//h5[contains(@class, 'ban hot') and text() = 'us states']"));
Option 4: Index the grouped selector (XPath only)
Limitations
Example:
driver.FindElement(By.XPath("(//h5[contains(@class, 'ban hot')])[3]"));
Option 5: Find the hidden list items link by href, then traverse back to h5 (XPath only)
Limitations
Example:
driver.FindElement(By.XPath(".//li[.//ul/li/a[contains(@href, 'geo.craigslist.org/iso/us/al')]]/h5"));