There's one big difference between the two groups, Indians care more about what's going on in the communtity more than the government. The people of Guatemala are quite poor and undereducated. Until about 1821, only wealthy and elite people went to a real school. Northern plains are very scarcely populated and incredibly underdeveloped. Probably not a place you might wanna visit.
Pacific lowlands are mostly farm country.
The best spot for you would be the highlands. It's got beautiful mountains, which are a blast to hike, and they have nice green hills. The only problem is there are occasional earthquakes. If you stop by there, you should go see the Volcan Tajumulco. It's the highest mountain in Central America.