Which smartphone is best for me?

Moin first.

So I have spent the last few years always with Android phones (first Sony and twice Huawei), but because my beloved P8 Lite because of the rumgehänge was barely usable, my friend gave me her old iPhone 6S. I'm really excited about the phone, it runs fast, without jerking, the camera is fine and I got used to the operating system despite all the "restrictions" quickly, find it especially great that everything despite the age of the phone runs so smoothly.
Meanwhile, I'm very annoyed that the phone has unfortunately only 16gb, which are not known to be expandable, and I can hardly or no longer use all apps and games, although I regularly draw pictures, videos, etc. On the PC,

So much for that, well I've been thinking that I need something new, preferably with at least 64gb of memory, but now the big question: Android or Apple?

I use mobile phones for an average of 3 years, or until you can still use them, without a nervous breakdown, for example, by hanging operating systems.
Does a used iPhone make sense? Will not pick up a cell phone which has the price of a small used car (iPhone 11), but also does not want that the phone hangs after a few months, as is the case with Android too often (1000 euro Samsung included). There are mobile phones from Android with 64 GB or more for about 200 euro (P30 lite z.b), but I do not know if just because the typical Android taste will occur again.

Need urgent advice people and thank you in advance

A refurbished iPhone 8plus you might like!

alternatively the cheaper 6s plus.

I'm satisfied with the S9 (64GB) and have a 400GB card in it. Memory problem? What's this?

Normally, a newly released iPhone gets five to seven years of system updates and so long it holds at least once or twice with battery replacement, unless the user has previously suffered a nervous breakdown, but this is not to be feared.

So far, the (new) apps on iPhones have become a bit leaner with every system update, which in itself has to be counteracted by the subsequent three-year shopping.

With an iPhone with 128 or even 256 GB of hard drive you should get along over the above period, but this memory can be extended even more. Apple calls it a necessary SD card iCloud. It is available as a cheap subscription and completely wear-free. Only the internet is necessary for that, but you always have it with you nowadays.

Yes, a retouched iPhone 8, 8 plus or XR would probably be right for you, depending on your budget.