Cuda OpenCL comparison cuda, openCL, nvidia

I was wondering if anyone could recommend a good comparison of CUDA and OpenCL. I was wondering if it is better to start a new project with OpenCL as opposed to CUDA. OpenCL seems to be more portable than CUDA but will probably lag behind in terms of advanced features. It seems to be that for an application programmed with CUDA there’s the slight disadvantage of requiring the user to have access to NVIDIA hardware, whereas with OpenCL the end user could use almost anything. Is there a performan…