Allow me to make a few comments, they might be helpful.
I have tried the following:
iPad 1 (non 3G - used with GNS 5870)
Samsung Galaxy Tab (7")
Samsung Galaxy S2
Samsung Note
Software wise I have been using Air Nav Pro but recently switched to Sky Map in connection with Flight Planner.
I have a mounting unit for fixing the iPad to the yoke, the problem is that the original iPad is so large that it covers quite a few other instruments. Additionally, the yoke mount is "ok" (just) for Cessnas but on modern Pipers it doesn't fit well. The Galaxy Tab was ok from a size point of view so anyone who has an iPad and thinks they are too big will probably prefer the iPad mini - however the Tab is rather large and cumbersome compared to a mobile device like a phone.
The Galaxy S2 was - in my mind - too small with Sky Map running on it but had the advantage of being portable. Additionally, the battery life was limited - I had bluetooth on, streaming music to my Zulus whilst Sky Map was ensuring I stayed away from controlled airspace which all meant the battery was pretty much dead after 3 - 4 hours. Yes, I could charge it from the power socket but do I really want cables draped around the plane?
Which leads me to my current favourite - the Samsung Galaxy Note. In terms of size it is optimal, fits in my pocket and yes, although it is rather large for telephoning, with Sky Map running, it gives you an overview of everything in your vicinity, allows you to quickly read off your location - none of this "ah... uhm.... er...." when the controller asks your current position and it also lends itself nicely to being mounted on the yoke.
I have two exchangeable reverse sides, one of which has a velcro strip stuck to it. When flying, I peel off the normal reverse side, put the side with velcro on. On the Piper yoke, I also have Velcro strips attached and, when getting in the plane, just press it into position in the middle of the yoke - in full view, without blocking any other instruments - quick and easy. And battery life is significantly better than the S2.
My vote goes for the Note and Sky Map any day, am hoping to get some air time this weekend, will take a picture of the Note in position with Sky Map running and post it, if anyone wants to see it.
By the way, I rarely use the GNS5870 in the Piper, the Note has yet to lose the GPS signal, indicating it sees between 9 and 12 satellites. I have yet to trial it in the Cessna - seems I prefer flying Archers these days - but had my Galaxy S2 in a jacket pocket slung on the back seat of the 172 and it recorded the whole flight easily without losing the signal. The reason for not using it is simply I use the Bluetooth connection from the phone to stream music to my headset, I couldn't do this with the GNS connected.....