Hi, for the LC ones the HPT midstream are actually more sensitive (10mlu) and the strip ones are 20. The midstream are also more expensive (for lullaby conceptions). I find the brand to be very reliable so i dont really think it matters which ones you buy - depends on cost i guess
As for the OPK's i'm not 100% sure on their strenght but i use the strip ones and always get great +ves but they will tell you on their website, Good luck