Well, you can't beat the Bitshares exchange as far as speed, scalability, provable reserve capital and collateral requirements, and of course its decentralization.

Keep in mind, that the User Issues Assets (UIA's) that you see listed on the exchange are tokens created by third parties, so some discretion will need to be used when choosing which of those issuers' tokens you want to invest in or even trade.

Smartcoins however, are market-pegged assets (mpa's) and are owned and controlled by the Bitshares platform/exchange itself, so you don't have to worry about some scammer CFO stealing your money or something. Smartcoins are also nice because they can be used as stable investment instruments for holding wealth (like bitSilver for example), buying stuff at BlockPay merchants, etc.

Hope that helps a bit @michellerhey :)