I would always buys ClearBlue Digital - the one that shows the words "not pregnant" or "pregnant". There is no faffing about under different lights trying to work out if there is a faint line or not. They are more expensive but if you are worried I would spend the extra on getting one.
i did loadsa test i used all the expensive ones and ones people recommend and on tha t.v they all sed negative so in the end i went to the pound shop and got sum from there they worked for me they all cum up positve and where right. so my recomendation is use pound shop ones. sound cheap but they worked for me. xoxo