I'd personally say that you're wasting your time with composite models. At 6.4" it's going to be fuzzy and hard to read text on. If you only wanted MP3 and DVD, that would *just* do, but for full-blown computer use you're going to want to go at least analog VGA input, if not a full digital input TFT display.
Also be careful to check out the nits of the display (brightness) as a lot of them are like 120 nits which will get washed away very easily in sunlight.
Here's a better question:
How much do you want to spend on the LCD? Then I can tell you what (I think) would be best.