If your looking for an investment, the best long term investment is definitely a home -homes are easier to sell and gain more value per dollar invested. In some areas it is not practical to buy a home for a short term investment, depending on market trends and neighborhood statistics it might be best to invest in a condo (you can also lose alot in an unsteady market). Condo's hold more value than co-ops and are a good short-term investment. Co-op's are not the best for investments, they can be nearly impossible to sell and the value can often drop in a two-four year period. Although if you shop around and find a good co-op you can reduce the risk of losing money by paying a cheap 'rent' (mortgage+maintenence)! You can often find a good co-op with low maintenance and pay the same monthly payments as a cheap rental -so why not take a chance (if you can rent in the case of not being able to sell), if you lose a little it will be like paying a normal monthly rent.

Keep in mind that some co-op's won't let you rent if you can't sell it and you want to buy a home. Also, some co-op's reserve the right to some of the profit made on a sale! And if you are lucky enough to be able to rent your co-op, some require board approvals.