The thing nobody tells you about outdoor planters is that the one you love in the store window is probably going to crack by its second winter, and not because it was cheap. Freeze and thaw does something to certain materials that you only find out about in February, when there's a hairline split running up the side and half your potting soil dribbled onto the porch. You learn fast which ones were built for actual weather and which ones were built for a patio display in a climate that doesn't really have winter.
On color, I'll save you some trial and error: terracotta, charcoal, and plain concrete gray are the ones that still look right after the plant inside them has died back for the season, which, let's be honest, happens to all of us at some point. Bright glazed colors are gorgeous for about one summer and then they're fighting with whatever you plant next to them, or clashing with a faded deck railing nobody got around to restaining. Go with a finish that reads more like stone or clay than like paint, because paint chips and stone just ages. That said, glazed pots have their place if you've got a covered porch where they're protected from direct freeze, a sunroom doorway, somewhere they're not sitting in standing water all winter. Unglazed terracotta is breathable and forgiving but it's also porous, so it dries out fast in full sun and isn't the best match for anything that hates to be thirsty.
Sizing is where most people go wrong twice: too small, then overcorrecting to too big. A planter needs real depth and width for roots to actually spread, not just enough room to shove the plastic nursery pot inside and call it done. For anything meant to anchor a porch or flank a front door, measure the actual door width first and keep the planter at roughly a third of that, so it doesn't swallow the entryway. For a balcony railing or a narrow side yard, prioritize width over height, since a tall skinny pot tips in wind more often than you'd guess, usually at the worst possible hour.
Construction is the real tell between a planter that lasts and one that's landfill in three years. Check the drainage hole is actually generous, not a decorative pinprick. Fiberglass and high fired ceramic hold up far better than anything described vaguely as "resin," and a planter with a slightly thicker, rolled lip has usually been made with more care than one with a sharp, thin edge. Good joints on anything built from separate panels shouldn't show gaps you can fit a fingernail into.
Get the material and the size right, and a planter stops being a pot and starts being the reason your porch looks like someone actually lives there.