Carrying groceries, a bag, or daily essentials changes what kind of bike accessory actually helps, and the three common options suit different needs.
A front basket is the simplest to use — drop items in directly, easy to see what's inside — but it sits ahead of the steering, so a heavy or unbalanced load can make the front end feel twitchy at low speed. A rear rack spreads weight over the back wheel, which is more stable for heavier loads, and can carry either a basket or bags depending on what's attached to it.
Pannier bags mounted on a rear rack are the best option for genuinely heavy or bulky loads — the weight sits low and to the sides rather than high and central, keeping the bike's balance closer to normal even when fully loaded. For occasional light carrying, a basket is simpler; for regular grocery runs or commuting with gear, a rack and panniers handle weight far more comfortably.