I've done it both ways, and in the end, I think taking on notes on computers has the edge. But, whatever you do, take notes, don't try to be a transcriptionist! When you transcribe you turn off your critical mind and switch to a stenographer's mind--not a great way to learn the material.
I finished an LLM in Tax Law in 2008. It involved 15 different courses. The first quarter I took notes by hand because I was "old-school." After that quarter I started taking notes on the laptop.
My notes ran from 50 to 90 pages per class typewritten, and the handwritten notes were about 50 pages per class.
All the notes contain valuable information that I refer to weekly. The typed notes are easily searchable. With the handwritten notes, I ended up scanning them and adding tags to the pages of interest in Acrobat so I could search them too, but that took a fair amount of time.
As for symbols and diagrams, I always kept a note pad during class for that sort of thing. If you date the notes, you can scan and insert them later into your typed notes if you have a decent pdf conversion program.
As for distraction, I certainly noticed it. The sound of typing didn't bother me at all, but something else did. I noticed a difference from my law school classes in the old days (1989-92): it was that class interaction seemed subdued. I think it may have been because of students having their noses in their screens, trying to get down every word, instead of trying to learn what was being taught.
Finally, if you are going to get a new computer simply for school, you might look into getting a tablet computer with MS OneNote. Then you can take handwritten notes and have them already on your laptop. It even has fairly decent handwriting conversion to typed text.