It'd be preferrable to have a porcelain, enamel-coated cooking surface. It's hard to imagine that portable grills have anything else for a cooking surface material, as porcelain with enamel has proven to be the most efficient, both in terms of cost and in terms of time. In fact, both porcelain and enamel should be present in many places of the portable charcoal grill. For example, you also want to have something similar to steel with enamel coatings for both the plates and the legs. These ensure maximum durability and long life in your grill.
Since you'll be actively using charcoal during your grilling experiences, portable charcoal grills have a slide out ash tray type of piece that will make the cleanup job a bit easier for you. However, you'll have to note that charcoal grills by nature are still the messiest out of all types of grills. These charcoal grills will usually not have a tray to catch the drippings, and they will stay on the porcelain cooking surface until you decide to clean it up.
Last but not least, it's got to have a cover. The only way any charcoal grill could inject a nice smokey flavor into your food is through having a cover or lid. If a grill doesn't have one, it might as well be an extremely messy and inconvenient gas grill.
You'll never go wrong with portable charcoal grills if you like both a smokey flavor in your food and an enjoyable cooking experience.
Check out the reviews of Weber portable gas grill, best portable gas grill, and portable barbecue grill.