First, you've come to the right place. There are people here who visit the island regularly, and even some who are there right now.
To address your concerns regarding the sargassum at Orient, I was there yesterday. There are areas where the sargassum is removed daily, so it's not a non-stop strip of seaweed on the sandy shoreline. Several restaurant-and-bar-and-beach chair companies rake it away each morning. It was a non-issue for me.
Also, all beaches on the island are open to anybody. No hotel, bar, restaurant, person, or company, owns any section of beach. You can go to any beach, pick a spot, post-up and chill. I rent chairs and an umbrella for my stays on SXM, and that's exactly what I do.
Advantages of Simpson Bay: It's walkable. Grocery, restaurants, bars, beaches.... all right there, walkable. However, though most other resorts in the area have direct access to a beach, Simpson Bay Resort does not (there's a metal walkway over large rocks, down to the sand-bottom bay). Hilton Royal Palm is very nice, though not cheap, with a great bar and restaurant. All large resorts in Simpson Bay have very nice pool areas.
As others have said, Orient is also walkable, and it's a very large beach, both long and wide. Lots of stuff for younger (and older) people to do. Also walkable.
My style is more Orient. A lot of Simpson Bay seems like Clearwater Beach or Daytona Beach or Fort Lauderdale. Lots of hotels, traffic, people, casinos, commerce. Whereas Orient has a more chill vibe. No large resorts. And it's very French... I mean, it seems more like a different country, whereas the Dutch side (in a lot of ways), sometimes has a "kinda USA" vibe.
My two cents. As I said, I'm on the island now, AMA.
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