If you know for a 100% FACT that you and her are completely clean - lambskin. It does NOT protect against STDs and has the most natural feeling of anything I have ever tried.
They cost a bit more, they might smell a little funny, and they're usually drenched in lube, which makes it fun to put it on while hovering over a chick's belly
Once it heats up it seems to adhere to your dick like a second skin. Heat and sensation transfer is great for both people.