Hi, I have used the clearblue ones and more recently amazon do some really cheap, non brand name. Although being quite naive I thought if I bought the sticks and got a positive result then I would have getting pregnant sorted. hum.. blatantly not!
Also, not sure its great to be pinpointing when you are trying for like 2 days a month, which I found I started to do. But I did find it comforting to at least know that I was ovulating, and doing something constructive.
But in terms of reading them, I have had the same as you, so for the first day nothing, next day a very faint line, like almost not there, then the third day I got a stronger line but its never as much as what the leaflet says.
best of luck to you.