I found a great recorder called Screenium. It's a recorder that costs only $40. If you don't wanna buy it however you can just google serial numbers. I get almost no FPS lag with it and it lets you record a specific window instead of a full screen.
To check your ram click the apple on the top left, then about this mac. Where it says "Memory" it should say like, 2GB or something. If your're only running at 30 fps, odds are whatever recorder your gonna use is gonna drop you down to at least 25fps. So, as far as screen recorders go, screenflow and screenium are the best ways to go. Neither are free as far as I know.
My memory is 4GB and Quicktime lags mine craft out when i play and record. I am on mac and i don't know what to do.
I have a very laggy computer, in general, but I downloaded the free trial of iShowU HD, and after tinkering with the settings (video quality, etc.), and the Minecraft settings, I eliminated most of the lag. I sacrificed some of the quality in the process, but the worst of the lag is gone now, and it's pretty good. If you don't want to spend any money, it's probably the best option.
Hope that helps.
Try camtasia, the most common reason for lag while recording is because you are playing and recording off of the same hard drive. If you have a desktop try getting a second hard drive in and then use fraps because it is better quality then camtasia. If you are on a laptop you will have to stick with camtasia. One thing to note is that camtasia DOES NOT record if you are playing in full screen.
I use Snagit and Podcast and/or Quicktime do not work for me. The map and some blocks disappear and the textures like water chests and the terrain a couple blocks away flicker like crazy its really aggravating, Snagit has a 30 day trial and ill prob try some new stuff but for the next 20 days Snagit is my main choice.
Screenflow is far and away the best! It's a bit pricey though but you can easily edit in it too!
I did this video recording and editing within screenflow. Even the intro! It's very easy to use and can do a lot of advanced things. It also doesn't give me much lag.