I've been through a few brands and always come back to D'Adarrio's, not exactly sure why, but they're just right for me.

Strat's love heavy strings. The heavier they are the better it will sound. Once you find a brand you like use the heaviest gage you feel comfortable playing. I've also noticed the trem keeps the strings in tune better with heavy strings. If you're using 010's, try a set with 011's or 012's and go from there.

I think it was standard bullets 009 I've had the last time.. Like them very much