I have Good Sam partly because I get discounts at the Flying J for fuel and propane (there's a Flying J close to the house). I've also used it at campgrounds and have been happy with the ones I've stayed at.
I also have a KOA card and more than made up for the cost this summer. Some of the places I stayed at were nicer than others, and one KOA which was very clean and well maintained, was older and had sort-of weird hook-ups. They all were fine for short stays, and the one I stayed at in West Glacier (in a deluxe pull through site) was one of the nicest places I stayed at while traveling through the western US and Canada. And I agree about the on-line reservation system - it works very well and is so easy to use.
I also have Passport America and recouped the cost of it this summer, though I only used it twice (once was off-season for 5 nights in Moab, a big savings). It has far more restrictions and I found it harder to use places, while Good Sam and KOA were easier.
I'm not particularly interested in membership campgrounds like TT, Coast to Coast, etc, though I realize that they are a good fit for some people. I stayed at one Coast to Coast campground in Kelowna, B.C. that was really lovely, sites had lots of room, all paved, 3 swimming pools, a small beach on a lake, along with their own dock, club house, baseball diamond, adult senior center, etc. But I don't need all that stuff, really - just a clean, safe place to stay with working utilities.
All of the clubs/memberships can be useful but only if you use them. I joined Good Sam even before I picked up the trailer - I'll probably recoup much of the annual cost just in gas savings at the Flying J because it's so convenient. So that one I'll continue to keep.
Until I stayed in Moab at the end of August, I thought that Passport America wasn't worth it for me, and I'm still not sure I'll get it again. I'm hoping to take another long trip this year, so will most likely renew my KOA card.
I didn't find getting used to the extra width of the trailer that big of a deal (I was very aware of it/scared about it before I actually towed my trailer). I have to use mirror extenders with my tow vehicle and that keeps me "honest" as far as width. My only other towing experience was with a horse trailer 30 years ago and only vaguely remembered, so I approached towing as a newbie. The big thing I remember from that experience is that you can't use your indoor back-up mirror, frightening for me the first time I tried to use it and all I could see was trailer! It's no problem using your wing mirrors.
I have an Anderson hitch and love it - I can carry the hitch head and stow it in the trailer's front storage compartment when I'm not using it, plus there's no bars to keep track of. It's simple to set up and works well for me, I don't have any experience with other WDHs.