I have been a member of both. I don't think one is better than the other, but they are different.
I've been to one MOA national rally & one RA national rally. The MOA rally had three times the number of attendees (over 6K) and maybe four times as many vendors than the RA. The RA had more Harleys show up. Not worse, just different. I saw a lot of the same bikes in the vintage show, and saw some of the same people at both.
The magazines are quite a bit different (my opinion). The MOA "Owner's News" (monthly) has a lot of ride reports, usually very well written, and I think more articles. The RA "On The Level" (I think every two months) has a lot more pictures of events, but also some good articles.
You can join the MOA and get the first three issues of the Owner's News and cancel your membership before the three months are up and owe nothing - so you can try it out for free. Since the MOA offers a digital version of the magazine, you can also look through (or download as pdf) the last five-years' worth of magazines. The MOA also offers the Flea-Market for members to sell stuff, and a pretty good forum. The RA also has a forum. The MOA publishes the Anonymous Book every year which is a listing of MOA members who will help you out on the road. It can be worth it's weight in gold if you have a problem a long way from home.
Our local BMW club, East Texas BMW+ Motorcycle Club, is affiliated with the MOA, but no longer with the RA. The only reason we dropped the RA is because we didn't have enough local RA members to qualify as an RA club (you need three). We only have about 15 members total, and six or seven are MOA members. I've been an MOA member for three years.
