Tweriod is one of my favorite Apps particularly for its simplicity. All you have to do is sign in with Twitter on the landing page and the App crunches the numbers for you to find your best times to Tweet. It will then show you the results on a beautiful graph and with all your key results in one spot. You can also go ahead and export your results via .pdf very conveniently.
Pro Tip: Tweriod also gives you some great additional analysis showing you different optimal timing for different days of the week. I found this very powerful.