mrShrimp:
Sorry, so just to clarify, you are suggesting that I should use an AVR Microcontroller (not Arduino?) because they are more newbie oriented? What AVR would you suggest for maximum memory storage?
Rather than saying "maximum memory" perhaps specify how much RAM, EEPROM, and program memory you actually require. An external SD card is always an option.
The Arduino uses an AVR processor so they aren't exactly mutually exclusive.
... but my project is to launch a HAB ...
I'm guessing a high altitude balloon?
The difference in weight (if any) of a couple of grams won't make much difference, I would have thought. However in any system the more memory you demand the heavier the chip will tend to be. But really, if you are just measuring stuff, storing in a (say) 4 Gb SD card will give you all the storage you need, so a cheap simple processor (like the Atmega328P) should be perfectly adequate.
A 2 Gb SD card I have here weighs 1.7g, so if your balloon can't manage to carry a chip of around 2 grams you have problems.