To me this is a big deal, so I am going to ask this question here. I want to know what the difference is between having a penis and having a vagina. A little bit about me is I am still pre op. The only surgery I have had done so far is a bilateral orchiectomy. The bilateral orchiectomy has done some good in my life, though still having a penis is the source of about 90% of the problems in my life.
I think alot about this. I am in such a position in my life where my dream of a vaginoplasty could come true as long as I just keep on doing what I am doing and keep my focus in the right place.
Is the difference mostly psychological, is it the ability to have the right kind of sex, or is it a little bit of both? Any input would be greatly appreciated.

One is an innie and the other is an outie.

All kidding aside you have correctly noted the differences.  I had bad dysphoria so the change for me was mostly psychological.  And I'm older so the sex part just isn't that important (I now that sounds weird).   Having GRS removed the one huge obstacle in my head to living comfortably, which I do now.  Keep dreaming and it will come true for you.

My outie thinks it's an inny. It hardly ever pops out unless I pull it out. The orchi will be booked in July and I'm going to see if they will tighten up the sack a bit while they are working. I'm good to keep the little guy for now as long as he stays hidden. I may consider a zero depth procedure after that somewhere down the road.

This may sound a bit simplistic. After having GCS I feel so much calmer ( I had no T per-op). My genital dysphoria is gone. The big difference is it feels right. I never think about my genitals now in a negative way, they just are there and are part of me.

Male genitals are less than 3 % of your total body, but they sure effect the way you think and act. Female genitals are internal and as such our behavior is much more accepting of what ever happens.

As for intercourse, the physical responses are similar and comparable, but not identical.

The honest truth? No holds barred?  A vagina is itchy sometimes, stinky sometimes, achey and mucousy and drippy and bleedy and.. ok those are the negatives. Most can be solved with a tube of vagisil, non fat yogurt, and pads. (Tampons and cups are a thing too).  Plus peeing you will usually be directionally challenged.

Positives? Well for one underwear fits wonderful as do dresses, swimming suits, etc.  Plus you can have a raging orgasm and not a soul would know otherwise... except you know the whole eyes rolled back, heavy panting, etc.. If you can avoid that noone can tell you are aroused.  And of course the whole internal receptacle for penises, dilators, vibrators, stuffed animals... oh wait forget the last part.   

On another note, never underestimate the impact of the labia or the clitoris as well.   The vagina is only part of the equation, sometimes a very small part when it comes to arousal (depending on the person of course).

Penises?  I'll leave that to the experts to describe in detail Its something I will avoid.  Frankly my experiences in this department are rather lacking anyways.

Wouldn't matter. Either way I would pee on myself.

The difference - for me, I absolutely hated one (penis), and I absolutely love having the other (vagina).  Oh yeah, and orgasms are waaaaaaaay better now, than the few I had in the before time (they're much more intense for me).

One nice difference, is that you can wear any style of female underwear and it just fits. I loved the idea I could wear those tiny g-strings.

Well sex is also better.. being penetrated is nice.. and the orgasms feel amazing.

Yes, in the beginning its a little bloody and peeing is a challenge at first. I wore pads with my panties for a long time after my surgery, even tampons for short periods when I ran out of pads.  Dilation is also no picnic, especially in the beginning.. but its so worth it.. as you get to have a vagina. I love my vagina.

The difference is: Night. And. Day.

To me the different was life and death.  I was walking to a bridge to kill myself because my partner would not accept me getting it done.  Fortunately fate intervened and I had the surgery.  And OMG to me it has been a huge seachange in my life: I enjoy sex immensely, I feel confident and happy about my body and I'm feel like a "real woman" - whatever that means.

Up front honest, though - my SRS result has been a textbook perfect dream result, and yours may vary.  That said, I feel I am (almost) as sexually functional as a cis girl and pretty much identical to my mother's factory issue equipment.  I self lubricate in a minor way, and I can orgasm through manual stimulation and penetrative intercourse.  I prefer it -very- rough, and even only 8 months post-op I can handle pretty much whatever my boyfriend does to it.

I am happy to wear onepiece swimsuits in front of my friends, and sexy lingerie in front of my boyfriend and playmates.  Nothing shows out of place.  Underwear fits perfectly.

But beyond that, it fits my mental map of myself.  It has quietened the demons that tortured me and makes me feel complete (well... as much as I can with out ovaries and a uterus).  Things line up in my mind and things make sense.  And that has taken me a long way to feeling like a real girl, like I fit in somehow and belong.  Like this whole thing wasn't a mistake or some mid-life crisis.

I feel so liberated and alive! <3

For a number of reasons very distracting to my life, sexual function involving my vagina has been something I have put off. That won't be forever. On the negative side of things, losing the penis removed something extremely stressful and wrong for me. Sure I could use the penis for orgasm but the mental consequences of having orgasm  were very unpleasant with a penis. On the positive side, I am just happier this way. I had a thread a long time back asking if people would treat me differently post GCS. I now have my answer and it is true, they do treat me differently. Right or wrong, I am judged to be more one of the girls by women. If there was any thought that I was a wolf in women's clothes, that is a non issue now. Guys I know who know about my surgery seem more free to treat me  as a woman. I suspect if they knew I had a penis still, they would have more fear (of being seen as gay) treating me as a woman. (Reporting here, not judging or agreeing with them.) I have more confidence using the women's room. More comfortable being seen in leggings. (Had first case  of camel toe. lol) It's hard to describe, but there is a decentralization of my thought process that happened without the penis. Other parts of my body are more important now, more of a body democracy than a penis driven dictatorship if you will. It is very personal at times, I will reach down between my legs at night and feel the  labia, the general flatness and it will just seem right, seem peaceful.
It is public sometimes. I wore a bathing suit to the beach and felt confident. I was at a hotel for my hair transplant recently and got a 'cat call.' My reaction was far unlike when I started early in my transition. I did not  feel like I  was playing a female role, I felt female. (Others are different, this is my feeling.) I was hiding nothing (penis, identity). I (again just me) feel more validated, genuine, confident in my femininity, and happy with a vagina.
All of the above is all about positive stuff. For my life there is a negative. Being equipped with female genitalia opens up new avenues of thinking that can be disturbing to your original place in the world. New thoughts can be very inconvenient. New thoughts that didn't exist before can happen.