Which Canon focus screen for using manual lens?

Hi, I have an EOS 3, which will allow to change the focus scree. I just bought a bunch of vintage manual lens. I was thinking of purchasing one additional focus screen, to facilitate manual focusing. I found these two: Ec-B and Ec-L. Which one should I buy, is it difficult to change it, and, will autofocus still work with EF lens?
Thanks!

There will be no affect on auto-focus because the AF sensors are not behind the screen. The exposure sensors are behind the screen and it's possible that if you're using a slow lens where the split screen blacks out then you may have to compensate the auto exposure reading slightly. Obviously not a problem if you shoot full manual.

Thanks Foxbat!