I'm mostly using the Responsive Design Mode tool which is built in to Firefox and Chrome.https://developer.mozilla.org/en-US/docs/Tools/Responsive_Design_Mode
I believe Isaac is doing his testing on an iPhone and the Nexus6; I'm attempting to do it on an iPod3G and a Nexus 6.
But the devices I'm using for casual on-device layout samples, are:
DEVICE -- VIEWPORT SIZE (portrait / landscape)
Nexus 5 -- 360 / 640
Nexus 6 -- 412 / 690
Nexus 9 -- 768 / 1024
iPhone 4s -- 320 / 480
iPad2 -- 768 / 1024
Microsoft Windows 10
Lumia 640 -- 320 / 480
** The viewport portrait width for the original iPhone (2G) through iPhone 5s is "320"
** The viewport portrait width for Nexus 9 and iPad 2 are both "768"
UBB.threads 7.6 is being designed around the recommended viewport ratio of 1:1
A full list of viewports (and screen sizes) can be found at:http://mydevice.io/devices/
I have several other/older mobile devices, but I don't believe there is any added benefit to also testing on those:
Google G1/Dream, Google ION/ADP2/Sapphire, Logitech Revue (GoogleTV), Google ADT1 (NexusTV), ChromeCast 1/2, Galaxy S1/S2/S5/S6, Galaxy Note 2, Sensation 4G, Nexus 4, Nexus 7 (2012), iPhone 2G/3G/3GS
Though, 99% of these devices are unnecessary for designing responsive platforms