I have an 11" 64GB MBAir (Dec. 2010) that I use as my travel computer. It has recently reached capacity no matter how many photos, songs, and documents I delete. Decided to get the newest 11-incher, w/128GB and backlit keyboard. The old one was running Lion (updated from its original Snow Leopard), the new one has Mountain Lion pre-installed.
I want to migrate my files from the old to the new one. Took forever to back up the old one via Time Machine (on vacation, used a 64GB thumb drive and after 24 hrs. the backup still hadn't completed; had to keep the thumb drive plugged in during the 7-hr. drive home and the backup never completed. Tried again at home, this time to my 2TB Time Capsule, which took 22 hours. After searching Support, I found out it was necessary to install Mountain Lion on it (which I also installed on my home computer, a late 2011 15" 750GB MBPro) before running Migration Assistant. I opted not to transfer via Setup Assistant on the new one simply because of the disparity between OSes and the need to back up the old one first. I have finally deleted enough stuff from the old MBAir to install Mountain Lion (10.8.2), and am now doing a subsequent Time Machine backup of it to my Time Capsule. Have yet to back up the new one because I intend to migrate from the old one.
My question is how should I accomplish the migration: restore the new one from the latest Time Machine backup of the old one, via wi-fi between computers choosing only designated files and programs, or via Ethernet (for which I'd have to buy a second USB-Ethernet adapter)? Or should I just sync my iPhone & iPad, use iCloud, and move selected files, programs & apps via USB thumb drive? (When I bought the 15" MBPro last year, I had the Apple Store migrate the data from my old 2008 MB Pro--AppleCare didn't cover it, and it was something I should have been able to do myself but was too lazy. Don't want to have to keep schlepping up and back to the Apple Store anyway.