What is the most comfortable postition to be Topped?

For me the best position for a newbie is doggy or also lying face down, kinda like doggy without you being on your knees. Its a great position and doesn't hurt at all, although i don't usually stay hard in that position (like in porno's when you see a t-girl hard all positions till doggy)

Lying on side (spoons) is also comfortable but not a personal fav

The sorest for me was missionary, i felt it hurt when it was inside me, and also its intimidating if the chick is large, because you look down and think 'how the hell can i take that'

I want to do way more anal in future and master the cowboy position.

For your first time I would actually suggest cowboy.

Yes... anatomically doggy style or on-your-side is 'easier' but for most folks the first time is more about being relaxed the whole time than anything else. And that's mostly in your head. So making it so you feel like you've got some control should help a lot. Takes some of the worry away.

The first time your goal should be to make sure you don't have a bad time. That's the worst thing that can happen so try and avoid it.

Have fun! And remember... tomorrow you'll know what she feels like!