To foil or to plastic wrap: that is the age-old question that's been around longer than I've known how to cook. So which keeps food fresher longer? The answer is that it all depends on what you're aiming to preserve.
Foil has a much more substantial thickness. It's preferable for aromatic, heavily scented foods like curries. It also prevents freezer burn, so use it for items that you're storing for a lengthy period of time in the freezer.
For fresh foods, opt for plastic; it's capable of sealing produce tighter than foil and is ideal for things like avocados and apples, which turn color when exposed. Aluminum reacts badly with acidic fruits and foods, whereas plastic wrap doesn't. Plastic wrap can even help to accelerate the marinating process.
It's important to keep in mind how you'll be reheating the food. It goes without saying that foil can't be microwaved, but heats well in the oven. While plastic wrap would melt under the heat of an oven, it seals in moisture in the microwave. If all else fails, there's always tupperware.