Are STD's harder or easier to pass during oral sex as opposed to vaginal or anal sex?
Depends greatly on which STD you're referring to. As far as oral, dental care is a minor but not insignificant factor. I'd imagine that vaginal and anal sex will greatly increase your chances (if you're not using protection). Orally, STDs aren't particularly easy to spread, but it's not terribly hard. Best advice is that it only takes one act to contract the disease so whichever you're doing, be safe!!
In regards to this do you guys where condoms when receiving (or giving) oral sex?
I won't give a guy head unless he's wearing one. If doesn't wanna wear one, I won't give him head.
Lastly what do those of you that use condoms for oral sex recommend as a good condom specifically for oral sex?
Brand and type depends on the couple because of allergies and whatnot. I don't have allergies so I use any of the flavored kind. Even if you don't enjoy giving oral sex, it's slightly less of a burden when the thing you're sucking on tastes like banana or chocolate or strawberry kiwi.