I've used Harry's Lap Timer, TrackAddict, Lap Timer HD and CMS Pro Lap timer. For a simple in-car timer, any of them will do. What else do you want to accomplish?
Harry's, TA and CMS can all also do additional functions like creating videos with data overlays (I've had problems with Harry's and video aspect ratios on Android), control an external camera (GoPro, TA also does Garmin) and OBD2 logging (throttle position, rpm, various temps & pressures) as well as use an external GPS.
For run-to-run comparisons, CMS Pro has the best data analysis features. By default the data overlays on video are not as polished as TrackAddict. CMS also does not require you to pre-select a track in order to get started, the others do, but many tracks are available, including Castrol. TA is made by the same folks that produce RaceRender - a great tool for producing high-quality videos with comprehensive data overlays.
I have the paid premium versions of all these apps and I mostly use CMS; often with OBD2 logging or GoPro activation and always with an external bluetooth GPS (10Hz resolution). Mostly because I like the data analysis features and I'm used to it. (It's data analysis is based on the MaxQData app that was popular a few years ago - "pocket PC" era...).