MBA camera or iPhone camera for analysing tennis shots in slow motion?

The MBA build in cameras wont do high rate frames per second needed for your purpose.

They are a web camera type and the CCD/CMOS chip is not of a kind that can do that, regardless of the software.

iSight is a webcam, with video capture at 30 frames per second in 24-bit color.

On the iPhone there is a chance since it has an improved camera:

The iPhone 5s has a 120-frames-per-second slow-motion video mode and precision autofocus matrix metering.

Sport events would use 300 FPS on a professional level with high resolution.

If you want to measure how fast you're serving you might want to get Tennis Camera. The app measures your serve speed in real time and reconstructs the 3D trajectory of your shot. An iPhone 5 or newer is required.

Disclaimer: I'm one of the devs behind the app.

Try ubersense app. In my opinion you do not need the high speed video cameras to get 99% of the info you are after. You can also use your iPhone from on top of the fence with a qm-1 from mytennistools.com