I've tried more software than I care to admit to. Evaluate them until you try all features and feel a program suits you.I downloaded a few free trials and settled on trying StoryBox because I preferred its interface to others. I've used it to plot and write one first draft, and I feel obligated now to purchase it, rather than just use the free version. But since I have a discount for winning NaNo, I'm considering trying Scrivener before committing to spending money on one or the other.
I've tried free trials, been happy and bought them (note the plural), only to find weeks later that this was not a wise choice for me.
Like you, my first consideration is the interface. My advice is: don't let it divert you from the availability and use of effective features.