What's better? Truecrypt or Encrypted disk image?
I would guess that the weakest link isn't the choice of formats, but your picking a decent password and not letting it get observed or captured.

In the general case where there is a system tool and a third party one, I usually start with the tool that is built in until I have good, definite and enumerable reasons to not use the default tool.

Go with encrypted disk images in the case you have set out.