Lava has the best burgers in Antigua by a country mile. Sure they may seem a bit pricey at first sight(they range from 40-65Q) but trust me they are worth every quetzal- you can go elsewhere for a cheaper burger but I can guarantee you'll wish you came here instead. Each burger comes with a generous helping of thick-cut fries or onion rings and a very generous side salad of rocket, fresh tomato and pickles. Not to mention the burgers themselves which are huge and come with generous toppings. You can tell from the first bite that they are made of 100% lean beef and are very juicy and done to your liking. The menu has a decent choice although not a massive variety of foods but, as the old saying goes, you should stick to what you are good at and Lava makes an excellent burger. You can find more variety in Ocelot downstairs which is owned by the same man (very nice man if you bump into him in one of his bars, he is the Welsh guy, Shaun).
In addition to the burgers Lava is also a very pretty outdoor terrace with views of the volcano and surrounding mountains. It has a great happy hour between 5-6pm every day with drinks from as little as 5Q and 10Q beers. There is also Sunday cerviche with 5Q sangria (and good sangria at that!). You can enjoy happy hour up here, have a great burger, watch the sun set then hop down to Ocelot for some live jazz most nights.
In short, come here! Don't worry over a few quetzales and enjoy one of the best burgers and happy hours you'll get anywhere!