Of course, I have already read various opinions on the Internet, looked at reviews, and simply informed me generally about the two smartphones.
My "problem" is that I've always had Samsung phones so far. On the one hand, I have always liked the smartphones best, on the other hand, I always thought that the brand is indeed not without reason market leader. When I talked to a friend, she came to the comparison, that even the majority of the "brand" in the sense of Ferrero, Milka, etc. Often finds better than the others. (Stupid example, but actually it's pretty much accurate - even if that sounds biased: I just always have the feeling that Samsung is higher quality.)
The battery of the s9 should be rather "mediocre", so you just come through the day. On the one hand, I think that it should (hopefully) be enough. On the other hand, with the battery on my current and my last cell phone, I had some difficulties.
What is your opinion? Which cell phone would you take or do you have?
Personally, I would opt for the S9 because I like it visually better (especially with the rounded display - that's just a matter of taste, of course). The P20 Pro would be a little too big for me. I do not own a cell phone from both and unfortunately can't tell you anymore. Maybe you're looking for a comparison between the phones on YouTube.
This is how the impressions differ. I bought my first smartphone around 2012 and everyone was already running around with Samsung devices. At that time, I looked at all the devices on the market and ultimately decided on a Motorola Razr. There were many other alternatives at the time and Samsung's only device, which I found interesting, was the Galaxy Nexus, which they built for Google. So the only device from Samsung, was for Google.
That's how it went today and I have not had to buy a Samsung device 1 time yet. If you ask most people why they have a Samsung smartphone, they usually do not know that many reasons, except "because I've always had that". And why have you always had that? "Because everyone else had that too?"
Before the big smartphone boom, Samsung (who was a junk maker at the time) did a good job of investing tons of money in marketing. Pay for advertising, advertising, advertising and distribution to bring Samsung devices into focus. That's what most other manufacturers have lost and that's why Samsung is where they are now.
One can say that Huawei is marketing technology currently in the fast lane and slowly burns in the heads of the people. The goal is then to sell devices without people thinking about why they should resort to a Huawei again in the following year. That's just brainwashing or better, very good marketing.
Long story short, look at what the market has to offer, what the devices can do better or worse, and then buy the device, which is better for your needs.
Personally, I would not buy any of the two devices right now, but if you put both of them before me and I had to decide, I'd PERSONALLY pick the P20 Pro.
Which smartphone would you recommend otherwise?
I think if you do not really need a smartphone right now, you can still wait for the next generation. Mate 20 Pro from Huawei will also be presented in the near future and then we're technically back on a different footing.
Personally, I'm also more fixated on the software and I would rather resort to a OnePlus 6. I just do not find Samsung's and Huawei's software very good and I would just bother that in everyday life.
Between P20 Pro and S9 I would opt for the P20 Pro, because of the much better battery life, the better camera and the much faster and more reliable fingerprint sensor.
You have informed yourself and know about the advantages and disadvantages of the two. It's up to you to make a decision. No one can help you here in principle. I can only give you the advice: Do not buy because of the brand. That makes sense only with Apple and that only because of iOS, if you want to have that. Otherwise, Samsung is a manufacturer like Huawei too. Both have corporate philosophies that you do not necessarily have to like. Just buy the phone that suits you better from the features.
If I had the choice between the two, I would take the P20 Pro. On the one hand because of the camera, on the other hand because of the battery. The battery from the S9 is quite a joke. However, the devices are priced anyway above the range, by I would buy a mobile phone.