The problem is the word "grill." A lot of barbecue terms can be very regional, and "grill" is one of them. In most of the country, a grill is an open grate directly over a heat source and is primarily used for direct, high-heat cooking. When we talk about grilling, we tend to mean food cooked that way.
Some people use that sort of grill for medium or low heat indirect by pushing the fire to one side, and putting the food on the other.
But in other parts of the country, a grill can refer to a dedicated, indirect, low and slow pit.
Do you want to do high-heat direct? Low heat indirect? Both? If both, which will you do more? Which are you willing to spend more on?
Some pits, like the better ceramics, can do an excellent job at both; but by and large pits which do both do one a lot better than the other. With respect, both BGEs and Primos are better grills than WSMs, and better smokers than a Kettle -- at least in my opinion. On the other hand, you can buy one of Weber's top kettles plus a WSM for less than the cost of a BGE.
How many people do you usually cook for? Do you frequently entertain large groups? How much capacity do you really want? How much do you really need?
Sometimes a bigger cooker can use different kinds of fuel than smaller ones. Do you care? Do you have fuel preferences?
What's your price range?
BDL