I used a few when I was pregnant and honestly most of them do the same basic job of timing contractions and calculating the intervals, so the differences are pretty small. Full Term and Contraction Timer & Counter are both well-rated and straightforward to use, while some mums prefer the one simply called "Contraction Timer" because the interface is very clean and easy to tap when you are in pain and cannot think straight. I would say download one or two now and get familiar with it before your due date, so when the real thing starts you are not fumbling around learning a new app lah. The most important thing is that it logs start time, end time, and interval clearly so you can show your gynae or the delivery ward team when you arrive.