There really isn't a best to be fair. There are opinions based on experience or personal bias. But there is GHL and Apex which are both popular over the counter closed ecosystems. Then there are some open source projects like Reef Angel. In between there are others but you sort of get the idea. I have used a open source based Reef Angel and it is more than capable compared to any other controller out there just not has nicely packaged. In fact, it does several things that the big two don't do or easily do such has new fish or coral acclimation with lighting by intensity or spectrum. On the other hand it requires more code skills or time to understand what you are doing. I also own a Neptune Apex and it is a nice little package. Does more or less what I want outside the coral acclimation thing I noted above. It is a one stop shop package that is much like Apple in they have products that just work together. Top off, dosing, etc.
I don't own or have used a GHL product but they look nice and have similar packages that work together like Apex. Like I said it is a personal preference and what you are comfortable with and how much you want to spend up front. You should build a list of what you must have in a controller then look at a couple different products and see if they check the box. If the do then you at least narrowed it down. From there just take the plunge. Best of luck.
Edit: Things on my list of must haves included hard wire ethernet port, pH, ORP, and Salinity probes, expandable, some sort of pwm management for lighting.