Does it help your chances at top colleges if you have a hard schedule senior year?
Yes… the rigor of your schedule is labeled as very important in the common data set for all the top schools.
But only take as much rigor as you can reasonably keep up with.
Thank you!
Also something to keep in mind…colleges only consider first semester grades in admissions (for RD), but they do look at your schedule for the entire year and expect you to keep it after you are accepted.
Take the hardest classes your teachers told you you can get As or Bs in. For instance, if you’re currently getting a C in precalculus, don’t take AP calculus 
but if you’re getting an A in Latin 4, take AP Latin. Check with your current teacher if you’re not sure.
If you think you’ll do poorly in a class, it is definitely not worth the risk of your class rank plummeting.