Most people spend just a few days or a weekend on the Pacific coast [1], though there’s plenty to see and do to fill a week or more.
For a quick beach break, Puerto Arista [2] and Boca del Cielo [3] are logical choices. Costa Azul [4] is another possibility—more isolated and scenic, but lacking lodging on the beach; unless you’re camping, the nearest bed is in Pijijiapán [5].
With more time, consider basing yourself in Tapachula [6] for two to three days; one day to explore the city itself, including the archaeological museum [7] and excellent restaurants [8], and another day or two to visit nearby sights like the Maya ruins of Izapa [9] and the beach at Barra de Cahoacán [10].
From Tapachula, several overnight trips are possible, including to Barra de Zacapulco [11], where you can take a boat tour through the impressive mangrove forests and enjoy the wide clean beach, or to La Ruta del Café [12], where you could spend up to three days touring various working coffee fincas.
Climbing Tacaná Volcano [13] is a goal for many who come to this area; it’s typically a three-day outing, starting from the small town of Union Juárez.
Links:
[1] http://www.moon.com/destinations/chiapas/the-pacific-coast
[2] http://www.moon.com/destinations/chiapas/the-pacific-coast/puerto-arista
[3] http://www.moon.com/destinations/chiapas/the-pacific-coast/puerto-arista/boca-del-cielo
[4] http://www.moon.com/destinations/chiapas/the-pacific-coast/pijijiapan/riberas-de-la-costa-azul
[5] http://www.moon.com/destinations/chiapas/the-pacific-coast/pijijiapan
[6] http://www.moon.com/destinations/chiapas/the-pacific-coast/tapachula
[7] http://www.moon.com/destinations/chiapas/the-pacific-coast/tapachula/sights/museo-arqueologico-del-soconusco
[8] http://www.moon.com/destinations/chiapas/the-pacific-coast/tapachula/food
[9] http://www.moon.com/destinations/chiapas/the-pacific-coast/around-tapachula/izapa-archaeological-zone
[10] http://www.moon.com/destinations/chiapas/the-pacific-coast/around-tapachula/barra-de-cahoacan
[11] http://www.moon.com/destinations/chiapas/the-pacific-coast/barra-de-zacapulco
[12] http://www.moon.com/destinations/chiapas/the-pacific-coast/around-tapachula/ruta-del-cafe
[13] http://www.moon.com/destinations/chiapas/the-pacific-coast/around-tapachula/union-juarez/tacana-volcano