i use liquid tests at the moment, but it may change in the future.
its just more cost affective to buy the api mater test kit at the moment for me.
the strip tests would be ideal, fast and easy to use. i have no idea how accurate they are, some say more accurate then the liquid tests because they have a preset amount of chemical set into the paper strip. but when they first came out a few years ago i was told they were not very good so just kept with the liquid tests. plus the strip tests at my LFS dont have a ammonia test on the strip so ide have to buy that spearate anyway.
never had a digital test, looked into it before but they were quite expencive and you have to re callibrate them all the time, sounds like far to much hassle.