Recently I had the opportunity to test both apps out. They are both are great apps and provide many readings for a vehicle maintence/repair DIYer.
They do require an ELM compatible bluetooth scantool transmitter. These can be purchased on sites such as Ebay or Amazon, just make sure you get an Official ELM chip and not a knock off. Quality devices run about $50.
I found that they both provide excellent and accurate readings of every vehicle sensor I could think of. They both also allow you to setup vehicle profiles so you can use the app on several vehicles and keep track of logs. Each can read and clear DTC codes (check engine light) and provide reference to explain each code.
The bottom line: Torque currently costs $4.99, Dash Command costs $49.95. While Dash Command has an easier to read and navigate interface, the $45 more in cost isn't worth it. Spend your money on Torque.