I had a GS3 for about 3 days... returned it. The screen was too big to use comfortably with one hand and, although I did like the options presented in Android, I did miss the level of polish that I've grown accustomed to with Apple.
I thought I would have that problem, but I like texting with one hand more with this phone compared to my iPhone for this reason... I can type SOOOOOOO much faster with two hands on my iPhone. So I usually do that...
With the GS3, I use swipe to text... which is used with one finger, in this case, my thumb. Also, for me, the size of the screen greatly offsets needing to use two hands sometimes.