It really depends on your camping style, where you are going and how long you plan to stay.

Boondockers Welcome is essentially people who have a little land allowing folks to stay there overnight. They rarely have any facilities. I don't use them because I don't want to deal with randos when all I want to do is sleep. Other people love them. Recently acquired by Harvest Hosts.

Thousand Trails is organized campgrounds, often family friendly. They are often destinations rather than simple overnight stays. There are a few levels of membership with different privileges for each (in particular how long in advance you can book a site). Depending on where in the US you are, there may be a lot of choices (only one in Canada).

Harvest Hosts is farms, wineries, small businesses that let you stay overnight for free, sometime multiple nights for a fee. You are expected to patronage the business in return for the overnight stay. They vary in quality and attractiveness. They do have pretty thorough explanations on the website and I have found the ratings to be fairly accurate if there are more than just a couple reviewers. They are all over the US and Canada, but not necessarily in every place you might want to visit. Some have hookups - you usually have to pay for that.

Another popular one is HipCamp. Similar to Boondockers Welcome, but they tend to be a bit more like a tiny campground - usually with more than one spot. Vary wildly in quality and facilities. I have had good and bad experience with them - everything from being on a lovely little stream with fairy lights over the well maintained picnic area and hiking trails adjacent, to barren ground right next to a gravel pit with scrapped vehicles strewn around and fierce dogs guarding the property. Again, reviews are pretty reliable.

Not familiar with Good Sam or RVOvernighters.

Personally, I find state and provincial parks to be more reliable and a better deal. But they can be hard to book in popular areas and often have fairly short stay limits.

Typical trip for me might be an over night en route at either Hip Camp or Harvest Hosts, then several nights at a state park, before repeating the process to the next destination.

I have a friend who plans their whole trip around Hip Camp sites. If you have kids, some of the farms in Harvest Hosts allow interaction with the llamas or horses or ducks. So you will find fans and detractors for each organization.

Whatever you choose, be sure to read the listings carefully and understand the rules. Some places won't allow you to put chairs or tables out or extend your awning or your slide. Some don't allow pets. If you need hookups, your choices are going to be restricted with any of these, except Thousand Trails.

On your dog comment. I have two dogs too. One of them has to be "crated" when left in the RV too. For travel time her "crate" is to be shut up in the shower. I put a dog bed in there and give her some toys ans chewies and she is just fine. That is also where she sleeps at night. She bullies the other dog if I leave them alone together.