Strings are like underwear. It doesn't matter what other people like, it matters what you like. That being said, buy electric "9's" for the strat. You can get a decent set for about $5.00, the most popular brands are Ernie Ball, D'Addario, and GHS. Save the outer package, take a few notes, how they feel and sound, if there's something you like or don't like. Next time try a different set, and keep trying different sets until you find your favorite. Same thing with the acoustic. If you have all metal strings, get "12's" if you have nylon strings, get "normal" tension. NOTE: if your guitar came with nylon (3 plastic-like) strings, then you MUST replace them with nylon (ask for classical) strings.
I started playing guitar about 25 years ago and just a couple of years ago I tried a new brand of strings that I LOVE, but only on one of my acoustic guitars. I still use "my" old brands on my other guitars. That's right, 3 different acoustics, 3 different brands. It's what I decided I like.
Last but not least, it never hurts to have spare sets on hand at any given time.
Playing guitar for 20+ years