Hi OP, this is a huge decision and I'm not surprised you're feeling stressed. My short response is that there is no 'right' answer so dig deep into what feels best for you.
Here's the longer response:
For many women, the urge to experience pregnancy and birth, and mothering a young baby, is very strong and shouldn't be ignored. Adoption can't give you this. Another thing to bear in mind is that, depending on your age, trying donor conception before adoption is more feasible than the other way round.
I had my first child through donor conception and the second through adoption. Both involved a ton load of ethical considerations and a commitment to continuing dialogue with the dc about biological, social and legal parenting. Our situation was quite different to yours, though, as we were a same sex couple from different ethnic backgrounds, so we would never be able to present as a 'normal' family. We also chose a known donor who, 20 years on, is still very involved. (I was going to put 'fathering' then realised that it would sound as if he was having new bsbies, a very different connotation to 'mothering'.)
Clearly issues around identity and knowing are key, but be wary of reading too much into accounts on social media which may not be at all representative. Do your research carefully and bear in mind that there are no guarantees.
On adoption, I think netflixfan's post was far too negative. It's just not true that successful adoptions are 'uncommon'. However, I think it is true that the parenting outcomes that most MNetters aspire to - happy uncomplicated kid who is heading for university - are fairly uncommon for us.
Many adopters struggle to let go of the hope that, with enough love and stability, their children can be just like everyone else's. We learn that our 'normal' is different, that love is not enough, and that most adopted children need high intensity therapeutic parenting.
I love my adopted child to bits and would never not want her here. But raising her to young adulthood has been the hardest thing I have ever done and I am knackered. And yes, I worry about her future and whether I will always need to support her and the children she is bound to have very soon.
I never recommend adoption to people. But if you do it you will find love, you will parent very intensively (while the world around you sees you as a diluted copy of the real thing), and you will become a fierce advocate for your child.
If you choose the donor route, you will have a much more 'normal' experience of parenthood but yes you will have to face some big questions around anonymous donors - and be prepared for the possibility that your child won't see it the way you do.
All motherhood requires accepting enormous responsibilities while having little control of some key areas. Parenting via DC or adoption is this with knobs on. Best of luck with your decision.