I'm interested in what you decide to buy. I'd go with the the desktop, too. The big screen makes watching movies (especially ones with subtitles) much more use-able. I don't ever need to have the computer outside. If I had a telescope or needed to have it analyze a car motor, it would be different.
Why not buy a cheap laptop with an i7, nVidia video card, and a 120Gb SSD? Then, when you're at home, connect the big screen, good keyboard, and large hard drive with back-up abilities.
2nd Generation Intel® Core™ i7 Processor HD video playback , Intel Turbo Boost 2.0 Technology and Intel Hyper-Threading High-definition audio with 5.1-Channel Surround Sound output ATI Radeon™ HD 6750 graphics 8GB DDR3 memory, 1.5TB hard drive Gigabit Ethernet for wireless connectivity 16X DVD R/RW Superdrive Includes HDMI port, USB 3.0 ports, Digital Media Card Reader slots and function keys
However, while many other laptops use Super-TFT screens, which use a glossy surface layer to produce richer colours, the Lenovo has a matt TFT display. Images aren't quite as vibrant as a result but, on the flipside, the screen isn't reflective, so you can use the laptop outside.
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http://www.compusa.com/applications/SearchTools/item-details.asp?EdpNo=602037&CatId=4928
2nd Generation Intel® Core™ i7 Processor
HD video playback , Intel Turbo Boost 2.0 Technology and Intel Hyper-Threading
High-definition audio with 5.1-Channel Surround Sound output
ATI Radeon™ HD 6750 graphics
8GB DDR3 memory, 1.5TB hard drive
Gigabit Ethernet for wireless connectivity
16X DVD R/RW Superdrive
Includes HDMI port, USB 3.0 ports, Digital Media Card Reader slots and function keys