I've done both. Many people get to and maintain a healthy weight on WW. But from **MY** experience, when you plateau WW doesn't offer much help. You can eat at the top of your range, eat at the bottom of your range, change your exercise and foods.
Spark on the other hand gives you SO much info. You can up your protein and lower your carbs. You can see that your sodium is too high, which is probably causing water weight.
you can use BOTH. There are WW teams on Spark.