If you’re not sure that you’ll get an A, take pass/fail but take only 1 pass/fail class per year at most–meaning that you should take classes that you’re sure to get an A in. To get a strong recommendation letter, you will need to take enough serious classes with the recommender to give the person a strong image of you.
So: take hard classes in a major that you’re good at (so you’ll get As no matter how hard they are), or hard classes in whatever field you plan to get recommendation letters from, but otherwise take things that you’ll get As even if it is an easier class. Do not take pass/fail except in unusual circumstances, and not more than 1 per year
Of the 2 pass/fail classes that I took in college, one was public speaking (I would have gotten a B) and one was a history class that I thought that I’d bomb. I ended up getting the only A in the class, out of 30 people. So basically if you’re at a level where you’re getting nearly all As–which is where you should be in order to head to a top law school- you’ll have a study system down that will result in sterling grades no matter what the class is, so pass/fail shouldn’t really be much of a concern.