*By best we mean in terms of best value.
The Apertus project is a community that aims to bring the open source ethic to cinema hardware. They have also partnered with the Magic Lantern team who have done great work liberating the photo and video capacities of Canon cameras by modifying the firmware.
Apertus were successful in their crowd funding campaign and they will be bringing out the AXIOM Beta video camera in 2015 and hopefully the AXIOM Gamma camera as well. There are several options for image sensors and lens mounts and they may support a frame rate as high as 300FPS in 4K! See their AXIOM Camera page for more information.
The AXIOM team released a YouTube update on January 27, 2015: