Downside of chicks: space (indoors), time, and equipment (truthfully not expensive, though)
Upside of chcks: you're more certain of healthy birds, you know you're getting young birds that will have a full laying life, they're freakin' cute
Upside of grown pullets: eggs almost immediately, they're already grown
Downside of grown pullets: no certainty of age or health, they're not so cute anymore (unless you're into that sort of thing)
All things considered, I got my flock as grown birds. I'm not raising them for meat, just for eggs. So that's also another consideration. If I were raising them for meat, I'd probably try to find some 20 weekers and feed the heck out of them quickly, and process them between 6 and nine months. Either way, make sure they have quality food (also access to grass, bugs, etc.) as you'll get better quality meat and eggs.
Keep in mind, I'm not sure what your wildlife is like around you, but they're are A LOT more predators of chickens than there are of bees. No need for a bear fence (they aren't interested around here) but you need to think about protecting them from roaming dogs, raccoons, skunks, weasels, hawks, foxes, etc. (the list goes on forever)
It is worth it though. They're almost as fun to watch as the bees, and you just haven't lived until you've tasted real fresh eggs.