I'm carrying the Samsung Galaxy S 4 right now, as part of the 30 day challenge. For the most part, I'm pretty impressed with the device. I've long been a fan of the software goodies that come with TouchWiz, and the Galaxy S 4 includes more bells and whistles than ever. The verdict is still out on whether I'll carry it after my 30 days is up, but so far, I'm pretty pleased. I'm rocking the white frost color, which I personally prefer over black mist.
Sporting a 1.9 GHz quad-core Snapdragon 600 CPU, I'm pretty impressed with the overall speeds of the phone. I see some lag from time to time, but right now, I'm chalking it up to transferring stuff over from my old phone to the new one. For me, it's often a battle of beauty (HTC One) versus what actually works for my day-to-day life. I need the larger battery that the Galaxy S 4 provides, and as I said above, I really enjoy the software goodies that come along with the device. I'm also a big fan of the 5-inch 1080p HD display as opposed to the 4.7-inch on the HTC One - I find 5-inches to be a near-perfect size for my personal use.
Prior to the Galaxy S 4, I carried the Galaxy Note II for about six months (when I wasn't working on a 30 day challenge). Before that, I carried the Galaxy S III, and before that, a bunch of iPhones - 4S and 4 (believe it or not, I've never personally owned an iPhone 5).
Will I keep using it after the 30 days are up? You'll have to wait until the end of the challenge series!