Next computer

I'd really like a new computer.  Below, I listed some contenders.
The System 76 is the biggest, heaviest, and cheapest, and I like Ubuntu OS the best.

System 76 Lemur 4 Laptop

• Preloaded with Ubuntu
• $849 (with the RAM and Hard drive specs outlined below)
• 4.5 lbs
• 14.1 inch display
• 8 GB DDR3 SDRAM 1600 Mhz, 2 x 4 GB
• 120 GB SSD Hard drive

13 Inch MacBook Pro

• OS X Mountain Lion 
• $1499 (with Specs below)
• 4.5 lbs
• 13.3 inch display
• 8 GB DDR3 SDRAM 1600 Mhz, 2 x 4 GB
• 128 GB SSD Hard Drive

13 Inch MacBook Air

• OS X Mountain Lion
• $1299 (with Specs below)
• 2.96 lbs
• 13.3 inch display
• 8 GB DDR3 SDRAM 1600Mhz
• 128 GB SSD Hard Drive

Dell XPS 13 Laptop, Developer Edition

• Preloaded with Ubuntu
• Has "developer profiles", like one for Ruby development or Android development, that makes installing all of the components needed to develop a specific type of application seamless.
• $1549
• 2.99 lbs
• 13.3 inch display
• 8 GB DDR3L RAM
• 256 GB SSD Hard drive