The .com is always the safe bet. Add to it the relevant unique domains out there, like .tv, or .bike, .io, or whatever is relevant to your business. The .co address is much less interesting, unless it works well with your name. (so tib.co is worthwhile, but yourbusiness.co is not.)
Domain registration is cheap, if you are the first. It's expensive to buy from someone later.
If someone already owns the .com domain, make sure they are not a problem for you, as a competitor. They may well have a trademark, or at least a common law trademark on the name.