What kind of oil would you use?

I am not talking about synthetic oil, but whether to use 10w-30 or 10w-40. I've been told that I should use 10w-40 because my engine has 200,000 on it and the thicker oil helps seals and sticks to parts better. But I've heard that you should only use what the manual says. I'm wondering what is better to use. I have 10w-40 in right now though.
What do you guys use for your car(s)

I use Castrol 10w40 all year but I live in SC...

If i'm correct the manual says 5w-30...I run 10w-30 in mine because of how many miles, but my advice is pick a weight and type of oil and stick with it. Engines kinda get used to a certain type of oil.