Just an obscure bit of trivia about FD lenses, if you are using the camera's meter. It was designed for FL lenses, which do stopped-down metering. The early FD lenses, in order to be compatible with the then-still-prevalent FL bodies, provide a way to put them in "FL mode" where moving the aperture ring actually stops the lens down as you turn it. You take the longer silver lever on the back and push it counterclockwise in its slot until you meet resistance and there's still a lot of slot left. Push a little harder and it clicks into place at the end of the slot. Now it's in FL mode (though you won't see the effects until the lens is mounted on a camera.) To take it out of FL mode, simply push the lever past the click stop the other way. Canon also made a couple of lenses that uses a little lever marked "L" to hold the silver lever in place rather than the click stop - I guess for space reasons inside the mechanism.

Years later, Canon got rid of this feature, I guess because they figured the market for FL-capable lenses was no longer there and they could save money by not providing for it. When looking at actual Canon brand lenses, the way to tell the difference is easy: the lenses that can do FL mode are the older breechlock style with the silver lock ring at the mount. The ones that can't are the "new FD mount" style with the black mount and raised red alignment dot and the silver mount release button.

If I were you I'd probably just get FL lenses - they work exactly like you're used to and can usually be had fairly cheaply. But the supply of FD lenses is far more plentiful so deals abound there too. Just make sure you get one of the older breechlock style if you're using your camera's meter.