I'm not an expert in the area. I know that one major difference relates to the availability/price of Medigap policies:
Medigap Disability Insurance Eligibility with Social Security Disability [can't vouch for the accuracy of the article]
I think you'd be allowed to participate in a Medicare Advantage plan. But many providers don't accept Medicare Advantage patients (none of mine do). I would think in general that the less affluent the area where you live - the more providers you'll find who accept Medicare Advantage patients. But I could be wrong.
Also - most MA plans are HMOs that may have a limited number of "in-network" providers - especially when it comes to specialists. The only medical problem you mentioned was RA (so I'll assume that is your most serious medical condition - perhaps it isn't - but you'll get the general idea how to approach things). If you have bad RA - you'll need/want a rheumatologist. So you'll want to explore if a particular MA plan has any rheumatologists in network (it is in general very hard to find any rheumatologists - there are only about 5-6 in my metro area of 1 million+ - and 2-3 aren't accepting any new patients).
If you have bad RA - you will also want to explore your drug options in terms of coverage. Either through a MA plan - a Part D Medicare plan - a low income drug assistance program - etc. I know that drugs like Enbrel (end of the line RA drugs for severe cases that haven't responded to other drugs) are far from cheap.
It is something you'll have to explore where you live now - and also every place you might consider moving. Note that there are insurance agents who specialize in this kind of thing - and it won't cost you anything to use one. The one we have used is pretty good IMO. Robyn