It's all about personal choice, but it's also good to read up the actual literature from studies and reputable sites, as well as talk to experts including medical professionals versed on the topic.
Here's a good link about survivability of HIV in the external environment: http://hivinsite.ucsf.edu/insite?page=ask-01-10-20
Here's what the CDC has to say about it (directly from their site, and this isn't copyrighted since they're a governmental agency aka public information, so you can copy and pass it along at leisure) - the link will take you to the CDC's site about chance of transmission in various forms: http://www.cdc.gov/hiv/resources/qa/transmission.htm
CDC: Can I get HIV from oral sex?
Yes, it is possible for either partner to become infected with HIV through performing or receiving oral sex, though it is a less common mode of transmission than other sexual behaviors (anal and vaginal sex). There have been a few cases of HIV transmission from performing oral sex on a person infected with HIV. While no one knows exactly what the degree of risk is, evidence suggests that the risk is less than that of unprotected anal or vaginal sex.
If the person performing oral sex has HIV, blood from their mouth may enter the body of the person receiving oral sex through
* the lining of the urethra (the opening at the tip of the penis);
* the lining of the vagina or cervix;
* the lining of the anus; or
* directly into the body through small cuts or open sores.
If the person receiving oral sex has HIV, their blood, semen (cum), pre-seminal fluid (pre-cum), or vaginal fluid may contain the virus. Cells lining the mouth of the person performing oral sex may allow HIV to enter their body.
The risk of HIV transmission increases
* if the person performing oral sex has cuts or sores around or in their mouth or throat;
* if the person receiving oral sex ejaculates in the mouth of the person performing oral sex; or
* if the person receiving oral sex has another sexually transmitted disease (STD).
Not having (abstaining from) sex is the most effective way to avoid HIV.
If you choose to perform oral sex, and your partner is male,
* use a latex condom on the penis; or
* if you or your partner is allergic to latex, plastic (polyurethane) condoms can be used.
Studies have shown that latex condoms are very effective, though not perfect, in preventing HIV transmission when used correctly and consistently. If either partner is allergic to latex, plastic (polyurethane) condoms for either the male or female can be used. For more information about latex condoms, see "Male Latex Condoms and Sexually Transmitted Diseases."
If you choose to have oral sex, and your partner is female,
* use a latex barrier (such as a natural rubber latex sheet, a dental dam, or a cut-open condom that makes a square) between your mouth and the vagina. A latex barrier such as a dental dam reduces the risk of blood or vaginal fluids entering your mouth. Plastic food wrap also can be used as a barrier.
If you choose to perform oral sex with either a male or female partner and this sex includes oral contact with your partners anus (analingus or rimming),
* use a latex barrier (such as a natural rubber latex sheet, a dental dam, or a cut-open condom that makes a square) between your mouth and the anus. Plastic food wrap also can be used as a barrier.
If you would like more information or have personal concerns, call CDC-INFO 24 Hours/Day at 1-800-CDC-INFO, (232-4636), 1-888-232-6348, 1-888-232-6348 in English, en Español.