Hi Dan,
That's awesome that you want to write the GMAT and aspire to attend B-school, like so many here do (or already are attending B-school).
Ok so I've been a professional tutor for quite a while now, and my job is to teach people the GMAT. I've dealt with all types of learning styles, along with learning disabilities (ADHD, dyslexia, etc). I know for a fact that if you have ADHD, you get 50% more time or so per section. You need a medical document and the GMAC will schedule it for you.
As for classes versus a tutor, I think your best bet would be a tutor. Classes are more depersonalized, and work great for crammers typically or people who have backgrounds in Math (Mathematics majors, engineers, physicists, etc) and/or Verbal (english lit majors, lawyers, etc). Now, a GOOD tutor will ALWAYS help you more than a class-- but they are more expensive. That depends a lot as well, if you're going to be doing a lot of hours with a tutor, they are almost always flexible with their rate. About half of my clients have taken a class before-- Oxford, Princeton Review, Kaplan, even a few from Veritas.
As for finding a tutor, that's the fun part (sarcasm). Depending on your city, there might be a lot, or there might be none (I'm pretty much the only one here, city with a population of 100,000). Most of my clients are from a bigger city, an hour away, population of a few million. Most advertise on Craigslist / Kijiji. Just a tip: If their ad isn't well written and has bad grammar, stay away.
You're going to have all types of tutors as well. The really good ones (who charge extremely high rates, think 100-200 / hour, or more). Then you'll have the ones that you can't understand at all, because they can't even speak English. Then you have the ones that just lie their asses off and say they scored a high 700, and as soon as you ask for proof you never hear from them again. You can almost always tell if a tutor knows the GMAT-- they rarely get a question wrong, and typically take under 60 seconds to answer a question. They also are able to explain a concept in a clear and concise manner-- they are good teachers.
Then you have the low-ballers. Sure, they might charge a low rate, but that's most likely for a reason-- they can't get any business, for whatever reason. You get what you pay for.
My rates are high, but I'm flexible especially if my client is a student or has a family and money is tight. If there are any other tutors reading this-- funny story. So this guy calls me one time, says he wants to nail a mid 700, has a few months, and wants to do a lot of hours. Makes up some BS about how money is tight etc. Me, being the nice person I am, agree to lower my rate. Then we meet. He rolls up in a souped up Benz with $5000 RIMs, wearing Dolce Gabbana, Prada, Versace, etc. While talking on his bluetooth to somebody in the Middle East. Yeah... So you just have to ask around.
One thing I can definitely tell you is that even if a tutor brags about being affiliated with X or Y company, it really doesn't mean much. Most of these companies have abysmal results-- they're all about mass marketing, making a class, pumping out the same lectures and taking the cash and running. A private tutor will actually care about how you do, and will go out of their way to help you out (like answering e-mail/phone questions for free). Just TRY to ask one of these companies about their results-- they'll never tell you. One of my guys took TWO classes, paid over $3000, and scored an abysmal 480. He came to me and in about 4 weeks nailed a 640 (12 hours of private tutoring). He applied to Canadian schools, which is more than enough to get in anywhere here.
So again I would recommend a private tutor, given your learning disabilities. Make sure you pick someone experienced, and make sure you meet them as well (tutors like to meet their potential clients too-- it's not like we just take anyone on). I don't even bother with more than half of the people who want to be tutored, because they're not serious.
Just my 2 cents. Best of luck.