I generally use proper words in texts, but I'll make use of some shortcuts - "c u soon" for example, or sometimes I'll drop the apostrophe in you're etc. That last one is because on my current phone, it's five or six key presses to get the ', and I often overshoot, and get frustrated.
I occasionally find myself debating which of two words that mean the same is better to use - because a shorter word might take more key presses than a slightly longer one, depending on the letters. I don't have predictive text.