quietq

Honestly, your post did give me the clarity that I needed. That last question really put things into perspective and I ended up committing to School B. I turned down School A and while it was one of the most difficult (and heartbreaking) things I had to do, I know that B is the best choice for my future. I think your advice really helped me to realize I need to step out of my comfort zone for once! Thank you so much!

I just had to make a very similar decision. I went with the program instead of the professor. The program offered me more opportunities to grow and become independent in my own right instead of following in a fantastic mentor's footsteps really closely, which I think will be important to my development in the long run. It was a really hard choice and I appreciate your dilemma! There is a case to be made for either decision, so I'll just tell you some of the things I considered and maybe that will help clarify your thinking a little.
Something to keep in mind - it can be risky to go somewhere with only one advisor in your specialization. Professors move, life situations change, your needs change, etc. I would be wary of going somewhere with only one person you could imagine yourself working with. It's nice to have a reasonable number of peers learning alongside you and other mentors to bounce ideas off of. Connecting with people at other institutions could help, but they won't be as easily accessible as someone whose office is just down the hall. A great advisor is great, but they're not going to be perfect. You will be frustrated by them or disagree with them at some point in your graduate career, and having someone else to talk to will help at the low points. The short-term 1-on-1 special attention would be really wonderful in the beginning, but are you going to feel limited a couple years into the program?
Here's another hypothetical question I thought about a lot: Are your potential advisors at School B good enough that you think you'd be happy and productive working with them? Independent of the fact that you really like the professor at School A, do you have a compelling reason not to choose School B?

Update: I officially accepted Program A this morning. It was hard because I do feel like I'm giving up some of the short-term comfort I'd have at Program B, and because I went against my mentors' advice, but I feel really strongly that I made the better choice for my long-term career. This thread was really helpful in reminding me to take the long view, so thanks for that! There's nothing I disliked enough about A to justify declining their offer. Getting out of my comfort zone and becoming more independent will ultimately be good things, and the ceiling for my research there is substantially higher. Telling Program B was difficult, but it went well enough and I am relieved to have some closure on this. I hope I've made someone on the waitlist happy, at least! Thanks for all the great feedback.

I understand you don't think you are looking for compliments, despite saying earlier that you are unhappy as none of your professors so far have complimented your work. It can be difficult to come from doing very well in undergrad to struggling in grad school, as the different program requires some adjustment. A lot of people have this issue from high school to undergrad, and again from undergrad to grad. You're not the only person facing this, but that doesn't mean that you don't have to be self-reflective.
You said the comments from professors make you feel worthless. No one can tell you that isn't how you are feeling, but that is not 100% about the professor. How they communicate and how you interpret their comments both interact to make you feel this way. And because sometimes you can't change how they communicate, you have to either get out of that relationship if you can, or change the way you interpret their comments to preserve your sanity. I would recommend the second one.
The writing centre should be very helpful, and you can always google what books to read. I don't think anyone else should need to tell you what books to read in graduate school, but if you want some recommendations on books about writing, here are some below:
APA 6th Edition Manual - even if you are not in psychology this is very helpful with writing introductions, discussions, formatting tables, figures, papers in general, and it gives you tips on style and word usage.
Elements of Style - William Strunk and E.B. White - this is the major book about how to write well. it has been around for almost 100 years and still holds true today.
Sense of Style: Scientific Writing in the 21st Century - Steven Pinker - this is an excellent book by an excellent writer, who talks about communicating clearly and without jargon/excessive complexity. Dr. Pinker also studies these topics in his research, and has great talks based on this book that you may be able to find on the computer.
I hope these are helpful. I use all three when I train editors that work for me at our undergrad journal.
That's great that you are determined to finish this program. My recommendations from my other post still stand, because they should be implemented whether or not you are staying. What you've been doing so far hasn't been working well for you, regardless of your marks (that's not what I'm referring to), so you should make some changes before things get even worse. We all have to improve and constantly evaluate how we're doing and how we're feeling, so don't just continue to do something if it causes you stress and if you feel worthless. Change it instead of 'dealing' with the misery.

Update: I officially accepted Program A this morning. It was hard because I do feel like I'm giving up some of the short-term comfort I'd have at Program B, and because I went against my mentors' advice, but I feel really strongly that I made the better choice for my long-term career. This thread was really helpful in reminding me to take the long view, so thanks for that! There's nothing I disliked enough about A to justify declining their offer. Getting out of my comfort zone and becoming more independent will ultimately be good things, and the ceiling for my research there is substantially higher. Telling Program B was difficult, but it went well enough and I am relieved to have some closure on this. I hope I've made someone on the waitlist happy, at least! Thanks for all the great feedback.

I can't suggest an exact number to aim for, but you could look at the CVs of recent hires in your field to estimate.