That's an excellent question! For a couple living in an urban condo, I'd generally recommend a trash bin in the 8 to 12-gallon capacity range. This size strikes the perfect balance for most couples—it's large enough that you won't need to empty it constantly (think every 2-3 days with normal use), yet compact enough to fit comfortably in limited kitchen space without dominating your floor plan.
Many couples find that a 10-gallon bin is their sweet spot. It comfortably handles the waste from cooking meals, everyday packaging, and general disposal without becoming too heavy or cumbersome to manage. If you're diligent about recycling and composting food scraps—which I highly recommend for condo living—you might find an 8-gallon bin perfectly adequate.
Consider your habits too: if you cook at home frequently or generate more packaging waste, lean toward the 12-gallon. If you eat out often or are minimal waste producers, the smaller 8-gallon might serve you better. The key is finding that balance where your bin contains odors effectively between empties while fitting seamlessly into your condo lifestyle.