What are the best positions that don't hurt your girlfriend to lose your v-card with?

That's good that you care, remember lots of foreplay to moisten thing up down there and make it less painful for her, go for missionary-you on top.
Some people try doggy style on their first time but it's not advisable, it doesn't provide the intimacy you want for it.
Go really slow at first, and ask if she's ok if she seems in any discomfort.
Have fun ;)

i suggest missionary. and try to finger her a little first so that she loosens up and it doesn't hurt as much when you decide to stick it in

Please, please, do not forget foreplay.
*vital.
Then, treat her like she's a god. Make her feel special.
Show her that she can trust you.
My recommendation, missionary.
Take it slow, and ask before you enter or change actions.
She is in control, whether you're on top or not.

I would suggest just missionary, going really slowly. The first time I had sex, I started out on top and it was way too painful so we switched to him on top and it didn't hurt as much.

missionary and look into her eyes.

Go slowly. If her hymen is intact then, from what I understand, there may be a little pain regardless. If you are both ready and I mean really ready to have intercourse then start off by really getting each other very sexually aroused. A lot of foreplay such as kissing, caressing, massaging, oral, etc. will help to stimulate both of you. Honor her by asking permission when you are ready to enter her vagina with a finger, tongue or penis. If she hesitates then drop back and do something else for a while. If she says yes then again go really slowly.

If she says no she is not ready to do it at all then don't even try again that night/day/whatever. If you are into each other there will always be another time and you don't want to do something you will both regret.

Finally, make sure you are protected. There is no such thing as safe sex only safer sex.