Advances in semiconductor device during last few decades enable us to improve the electronic device performance by minimizing the device dimension. However, further development of these systems encounters scientific and technological limits and forces us to explore better alternatives. Low-dimensional carbon allotropes such as carbon nanotube and graphene exhibit superior electronic, optoelectronic, and mechanical properties compared to the conventional semiconductors. This Feature Article reviews the recent progresses of carbon nanotubes and graphene researches and compares their electronic properties and electric device performances. A particular focus is the comparison of the characteristics in transparent conducting films (transparency and sheet resistance) and field-effect transistors (FETs) (device types, ambipolarity, mobility, doping strategy, FET-performance, logic and memory operations). Finally, the performance of devices that combine graphene and carbon nanotubes is also highlighted.