Really, what to get is going to come down to your campaign. "Both" is a fantastic answer, don't get me wrong (Jason will beat me with a wire coat hanger if he hears me telling someone not to buy multiple books), but if you can't get both at once, to decide what order to get them in, I'd suggest thinking about what order you'll need them in.
Is your group sticking to one urban sprawl, getting tangled up in street level crime? Dealing with gangs, working for the mob, fighting Yakuza thugs, running drugs (or fighting drugrunners), and related "gritty" type stuff? Vice is very much the way to go.
Are you looking for globe-trotting action, instead? Do you want to fling them into neighboring countries, and cook up your own epic story arc that's based on the metaplot with little hints and clues from existing SR products and the timeline itself? Do they have international backgrounds you'd like to flesh out by knowing more about various countries in the Sixth World and global hotspots? T6W Almanac all the way.