There are roughly three levels in this market.
At the top are the original providers, developers and infrastructure owners who create the services and supply them wholesale. Below them are SMM panels, which aggregate and resell those services at very low prices. Panels are a bit like a rave: you are responsible for yourself. If an order gets stuck, drops or needs to be stopped, support is often limited and refunds can be difficult.
The third level consists of retail websites and specialized sellers. They usually source from panels or upstream providers and charge more, but the additional price should cover supplier selection, order monitoring, continuity and proper customer support.
For transparency, this is where I operate with Best YouTube Views. My advantage is not pretending that I own every traffic source. It is knowing the market, constantly comparing providers and evaluating services on my own videos before offering them to clients.
The best source is not always the same. Quality changes, servers close and performance depends on the niche, country, delivery speed and objective. I would also be cautious with anyone guaranteeing rankings, because views are only one part of the equation.