What are the differences (other than length) between OCS, State OCS, Accelerated OCS, and ROTC?

Having been a State OCS commander, there is no difference in the curriculum.

Your specific situation will dictate most of those answers. As LTC K. stated, the curriculum is the same for traditional state and accelerated OCS programs. ROTC adds military science classes that include more research based papers.

A lot of this might depend on how you want to complete the remainder of your college courses and how well you multitask. If you have the resources to complete college at a university and you don't need to work full time on top of that, I would suggest the ROTC route. You could participate in the Simultaneous Membership Program and drill as a CDT until you graduate. Again, I suggest this route if you have the means. If you do not have the means to pay for school and support your family, you may need to keep a full time job. If that's the case, you may need to go OCS. I would suggest completing all your college courses prior to applying for OCS in this case. From experience, full time job, traditional OCS, family requirements, and full time school was not a great idea. I had to drop my classes for Phase 1 and 3. Then again when I went to BOLC. I didn't finish my degree until about 9 months after BOLC.

I completed Phase 1 and 11 months of the 12 month Phase 2 of traditional state OCS. Then I completed Phases 2 and 3 accelerated. Results may very. So I essentially completed everything traditional and everything accelerated. From my experience, you learn more from traditional if you are a traditional guardsman. You will complete more assignments between drills. We had a monthly newsletter that required us to take turns writing articles on military leaders, books on the SEC DEF reading list, and interviews with local leaders. The month between drills was also used to plan events for the next drill and study for tests. Some drills have major events such as FTX and ruck marches. Candidate leadership plans these events and you need time to conduct leaders recons. Traditional programs also have a history of having much better staff rides. Plus, completing a case study between drills allowed me to learn more about the subject. At accelerated, I ended up writing it by hand on fire guard based on a couple printouts we were given.

If you're looking for what's easiest, I would have to say accelerated due to that being your full time job for that 8 weeks. The washout rate is much lower for accelerated as well. If you have completed BLC, you should have the basic skills to be successful in accelerated. However, it's not a given that your state will send you accelerated.

If I had to do it all over again, I would have gone to a university with my GI Bill, attend ROTC, applied to scholarships, and be done with it. I had about 40 college credits when I decided I wanted to commission. I went to school in evenings and online, started OCS at exactly 90 credits, completed most of traditional then accelerated OCS, completed BOLC, then finished my degree online over a span of 4.5 years. It would have taken the same amount of time to go to a university with an ROTC program and save me and my family a lot of stress.

Traditional is generally considered the hardest. So much time between drills, the mental switch required before and after each drill, and just the sheer amount of time that life can interfere. Had a friend who did both traditional and accelerated (long story) Nd he said that knocking it out all at once was way easier. No distractions.
That said, if you are staying m-day Guard, the traditional is best way to get used to that battle rhythm. It gets you used to all the additional demands that you are going to have as a drilling Officer.