[Last updated in 2014?]
I bought the "Android 4.0 Mini PC" (generally called the "mk802" online) in early July of 2012, my Raspberry Pi (original rev. with 256 MB memory, polyfuses, and no mounting holes) arrived at the beginning of August 2012, and I got a BeagleBone Black in May 2013. The mk802 is smaller and has onboard storage, but overall I think I prefer the Pi - in part because of the better (although not great) Raspbian distribution for it. (More notes below the picture.)
I've ended up with a great deal more kit, primarily cables and SD storage, running up the price of these purchases. The mk802 needs a mini-HDMI to HDMI cable (they supply it). If you want the mk802 to boot a Linux distro, you'll need a micro-SD card, and probably a big one: the distro I've found myself preferring has a 8GB image. The Raspberry Pi assumes you have a micro-USB phone charger as a power source - I didn't have, and you may not have what's needed either, as the Pi can draw up to 700 mA when many of the chargers provide only 500 mA. For the Pi you need an SD card (only 2GB this time) and an HDMI cable. A case is recommended but not required.
|Headless Toshiba laptop||Intel Pentium M 1700||20w doing nothing, 25w basic activities, 40w flat out|
|Acer Aspire netbook||Intel Atom N455||20w doing nothing (16w with screen off), 23w basic activities|
|Raspberry Pi B (original, 256MB)||Broadcom BCM2835 - ARM11, 700MHz||2-3w|
|Raspberry Pi B+||Broadcom BCM2835 - ARM11, 700MHz||1w|
|Raspberry Pi B+ with Adafruit 3.5" touch LCD screen||Broadcom BCM2835 - ARM11, 700MHz||2-3w|
|Android mini pc mk802||Allwinner A10 SoC - ARM Cortex A8, 1 GHz, Mali 400 MP GPU||2w|
|Beaglebone Black||TI AM335x SoC -> Cortex A8 1GHz, SGX530 3D graphics||2-3w|
|TP-Link TL-MR3020 (running OpenWrt. MIPS 24Kc V7.4?)||Atheros AR9331 400 MHz||0-1w (the Killawatt sometimes showed 0w! but no wireless)|
|Linksys WRT54G v2 (running OpenWrt)||Broadcom 4712 200 MHz||5w (no wireless)|
|Linksys WRT54GS v2 (running OpenWrt)||Broadcom 4712 200 MHz||3w (no wireless)|
Please note that the wattage values above were measured with a Killawatt, which I'm quite sure doesn't measure accurately below about 5w. Nevertheless, I think we can safely say that the Pi and the mk802 use very little power indeed (and the TL-MR3020 even less). The laptops were fully charged when tested.