LDPI HDPI MDPI XHDPI XXHDPI XXXHDPI

Brand	Devices		Pixel Per inch (ppi)
Samsung	Samsung Galaxy S6	xxxhdpi	577
	Samsung Galaxy Note 4	xxhdpi	515
HTC	HTC One M9	xxhdpi	441
	HTC Nexus 9	xhdpi	281
Huawei	Nexus 6P	xxxhdpi	518
LG	Lg G2	xxhdpi	424
	Lg G3	xxhdpi	538
	Lg Nexus 5X	xxhdpi	423
Sony Xperia	Sony Xperia Z3	xxhdpi	424
	Sony Xperia C4	xhdpi	401
	Sony Xperia C5	xhdpi	367
	Sony Xperia Z3 Tablet	xhdpi	283
Motorola	Moto G Turbo Edition	xhdpi	294
	Moto X force	xxxhdpi	540
	Moto X Play	xxhdpi	403
	Moto G 3rd/2nd Generation	xhdpi	294
	Moto E 2nd Generation	hdpi	245
	Moto E 1st Generation	mdpi	256
	Moto Nexus 6	xxxhdpi	493

How do you identify ?

You identify the category by just checking the DPI

ldpi - 120 dpi

mdpi - 160 dpi

hdpi - 240 dpi

xhdpi - 320 dpi

xxhdpi - 480 dpi
xxxhdpi - 640dpi

Will be updating with few more devices soon :) help me out if i am wrong or you can add some more devices in list if you know in which category the devices falls in.

Check out the version histories of Android
http://qualitytestingtips.blogspot.in/2016/02/version-histories-of-android.html