small warning here if you have a strat with whammy bar; if you're gonna replace your strings with thinner or thicker gauge as the ones it was originally then you have to readjust the guitar to that as in bridge hight, trusrod setting and action so look out with that.

As to what brand and type of strings entirely depends on what tone you are looking for, type of winding around the strings ( bronze, nickel etc ) and flat wound or round wound all make a difference in sound so experiment with different brands and types of strings. For me on my strat I use D"Adario's round wound bronze and sometimes I switch to Elexir strings only because of the nice feel they have; D'adario's become noisy when sliding over the strings.

Herman