Some apps are great for use in centers. Some are better for individual use. Some track student usage, most don’t unless you pay for it. Some tie into other programs such as BrainPOP. My best solution is three fold.
First, do like the kindergarten team and discuss apps together and decide which ones you want to use across the grade level. (Don’t forget to include support staff or at least supply them with a list of the apps you use)
Second, use app review sites. Here are my suggestions. There are many out there and I like to find the ones created with education in mind.
Third, share what you learned. I have a form here where you can review the apps you use. If you don’t have time then send the apps to me and I will put them in (it just won’t be as good because I don't use them in the classroom)
App review sites
Also don't forget about my website and Diigo list. Which are really the same thing in different forms.
A list of webapp review sites with notes on the quality (feel fee to add any you know)