Size & Portability
What you intend to use your grill or stove for obviously dictates to some degree the size of stove you need. If you regularly cook for a large number of people, then a two to four burner model will be more useful. For just a couple of people, a single burner may suffice. If you plan on using it on your RV or caravan holidays, then size and weight is less of an issue than it will be if you want to take it camping. You can find single burner gas stoves which weigh less than 5 lbs; some multi-burner models can weigh well over ten times this. Many portable stoves come with their own carrying cases, which can be a great convenience.
Usability
Obviously, no portable gas stove is going to be any use unless it can cook your food quickly and efficiently. Unless extreme portability is your goal, or you normally just cook for one, then a model with two or more burners is much easier to cook on. You may see a lot of references to ‘BTUs’ in a stove or grill’s specifications. This is short for British Thermal Units, and refers to the amount of heat required to heat a pound of water one degree farenheit. However, in this case it’s more useful as a measure of gas consumption than heat output. If looking for a grill, choose a model which has a sturdy rack with a fairly large gap size. Side tables are included with some designs, and they can be very useful. If choosing a grill or stove with a stand, then it’s vital to choose a sturdy one; there are some flimsy models that simply aren’t stable and are potentially dangerous.
Maintenance
Stoves and grills get messy very easily and it’s important to find one that’s easy to maintain. With a grill, a porcelain coated rack is much easier to clean than a poor quality metal one (though that’s not to say there aren’t good quality stainless steel ones on the market).