Just fitted one of these today:
http://www.ebay.co.uk/itm/302121603028?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AITI am not sure if it's the "best" as I haven't got anything similar to compare to.
If I did it again, I would probably try and get one with more memory - they now also do 2GB RAM models - not that this is slow, it pee's all over the Mrs 2015 Nissan built in system for speed and scrolling around, just feels a little sluggish at times when lots of stuff has been set running. May be a little unfair there, but think of it as a lower end Android tablet rather than a Samsung
Install was straightforward, there is a comprehensive amount of leads and connectors for just about anything you can think of - video outputs for rear screens, reversing camera, canbus interface, bluetooth, wifi, amp connection leads, proper antenna adapter for the dual VW standard one, USB extensions, external microphone. It also came with a connector to the mk5 USB port you can fit by the gearstick - just ordered one as it will look better than having a lead in the glovebox. Sat nav map SD card is also included and there is a second SD card slot for media or app storage.
The canbus stuff is pretty clever, no need to run loads of wires for a reverse signal. It also shows door/boot/bonnet open status on the screen automatically, some info from the car fuel gauge and temp is shown too. I believe it integrates with the multifunction steering wheel controls, but I don't have them on my GTI personally - maybe in future.
For good measure I also hooked it up to a OBDII bluetooth dongle and have extra gauges on the display through torque. Sat nav is quick to get a fix.
There are a million and one applications you can install on it if you wish, much the same as any Android tablet.
Screen is very decent and clear, and you can buy other bits for it if you wish to add DAB, TV tuner.
It really looks like an OEM unit IMO, certainly better than the Kenwood thing my car came with by a mile.
Build quality is good as is the fit, it looks perfect installed. If I am being picky I don't like the rotary knobs much - would prefer them a bit bigger - and the buttons are a little mushy compared to the Mrs unit in her Qashqai.
Anything else give me a shout