On my SGS3, I am currently using Swype. I love the new landscape split keyboard as I usually type in landscape. The auto-correct and text prediction is also very good. I am finding I type quite well on it compared to most other keyboards. I do occasionally type in portrait mode. I use the Swype gesture typing when typing in portrait. It is very easy to type one-handed this way. The gesture typing on Swype is better than any other keyboard I have tried by far.
I was using Kii keyboard for quite a while as my landscape keyboard. The 13-key landscape split keyboard is my favourite layout amongst all landscape keyboard. I find I can type in this layout better and with fewer keying errors than any other layout. Kii also has gesture typing, but unlike Swype, I cannot activate gesture typing in portrait only. Until recently, I used Kii as my landscape keyboard and Swype as my portrait keyboard. The inability to turn off gesture typing in landscape was the main reason I did not use Kii as my primary keyboard for both orientations. Once Swype came with a landscape layout that is similar to the Kii's 13-key split layout, I switched to Swype. Swype's auto-correct is also significantly better than Kii's.
I used to use SwiftKey as my keyboard. This was the first keyboard that I really liked for touch screens. I always preferred physical, landscape slider keyboards, but the industry has moved away from physical keyboards for the most part. SwiftKey's auto-correct/text prediction is simply better than any other keyboard I have tried. Swype has come close and Kii is a significant step behind. The reason I no longer use SwiftKey anymore is that I just hate the landscape layout. I find I make so many mistakes, especially hitting the space bar and shift key by accident. Keyboards in general cannot successfully auto-correct these types of keying errors. A better keyboard layout with a poorer auto-correct results in a better typing experience for me.