So the Android market is FLOODED with literally hundreds of models. Leaving one big question - which one do i go for????
Well, that really depends on what you want to do with your android TV Box. For a start they come in all shapes and sizes from a little pen drive that connects directly to your TV's HDMI port to a set top box style similar to that of an Apple TV or WDTV. There are pros and cons for both styles. But at the end of the day its down to personal choice and tastes, my personal opinion being set top box looks better.
GPU's, CPU's, Flash Drive, Ram...
Your choices of any of the above is purely based on the size of your budget. If you are looking to simply browse the web, playa few games and use XBMC then ideally a dual core CPU will do the trick just nicely. The larger the budget the larger the number of cores but it is generally accepted that dual core of around 1.5Ghz is more than capable. As for the GPU, most good boxes these days seem to come with the Quad Core Mali400 3D GPU and this does a great job. Of course you can keep it simple with a single core CPU and basic GPU but overall performance will suffer. Ram will vary for 512Mb - 2GB in some cases. Again deciding on what you want to do with your android TV is dependent on how much RAM you would require. For basic internet browsing then a single core CPU and 512MB of RAM will be fine, however for anything more such as running game apps or streaming for XBMC then such a low spec unit will probably not be, in most cases powerful enough.
If what you are interested in is watching HD movies either over the network (streaming) or off your own NAS/external USB Hard Drive then the more RAM the better. Get the most RAM your budget will allow, however in most cases 1GB will be more than sufficient.
So to synopsise – spend what your budget will allow! My personal opinion is set a budget for £100 and work your way down. A system with dual core and 1gb or above RAM will doe most things you would want a HD Media Centre,