Which type of investment is most likely to have the greatest long-term increase in value? Stocks and bonds. Stocks and bonds when a company purchases a new asset is one of the best long-term investments you can invest in. Due to them being long-term investments, the asset needs time to accumulate more value for what it's worth before you sell it. Long-term investments value tends to rise overtime and not often would a short-term investment hold if kept to long.