Quicktime offers easy to use screen-recording. It's one button (record) with a couple of settingo for video quality(medium or high) and the videos(.mov) save location
Depends on what you need to do. Screenflow is a nice app and easy to use, you can annotate, etc. If you just need to do a quick screen recording, Quicktime is a good choice. It's easy and you already have it installed.
I like Quicktime's new recorder, it's okay, but I also like iShowu. It's $20, but well worth the money. The quality is great, the audio is easy to use, and you can select which part of the screen to record, or do the whole screen.
Also compresses nicely in conjunction with something like VideoMonkey.