If your main concern is cost, then the Aspire S3 is hands down the better choice as it is priced at $900 versus the 13-inch MacBook Air's $1,300. You can, of course, get a MacBook Air that is closer in price to the S3 at $1,000. But for that, you have to drop down to an 11.6-inch screen and far less storage.

The new S3 has a solid state drive just as Intel hoped manufacturers would use for new Ultrabooks. Unfortunately, the SSD is just there to house Windows 7. For storing all your files, Acer turned to a 320GB hard drive. The MacBook Air, meanwhile, sports 128GB SSD. Solid state drives are often admired for their ability to significantly increase a computer's performance speed compared to a device with a traditional spinning drive.

Part of Intel's hopes for Ultrabooks is they would offer instant-on functionality similar to the MacBook Air. Acer says the S3-951 can resume from sleep in about 2 seconds and 6 seconds from what the company calls "deep sleep mode," which is probably just a fancy term for hibernate. Apple does not provide benchmarks for its so-called "instant-on" technology.