I use Quickoffice Pro HD, a $15 app which can import/export Excel and Word files, as an alternative to Apple's apps for the same functionality. I can take notes in ward leadership meetings and the iPad's touch-screen keyboard is reasonably comfortable to use. I have a 32GB iPad with Wi-Fi (and without 3G capablity) and it suits me just fine. I mostly fill the internal memory with music and video files. The other apps and data on the device don't really require much of the storage memory.
I also have high praise for the Gospel Library app (it's FREE) and all of the material available there. Like dwightbuchanan said, you can load up the teacher's manual for something like a Gospel Doctrine lesson and follow along. When it's time to refer to a scripture, there's a link in the lesson manual that will take you right there and then there's a link on the top of that page to take you right back to the lesson. Very nice and very fast! It's much faster than using paper books. If they call out a scripture that isn't near one of the links then it might take as long to find it as it would with a book. But with the iPad it's like you're carrying LOTS of books without all of the weight and size to worry about.
The LDS Tools app (also officially from the church and free) allows you to have directory and calendar data on your iPad at the ready even when you can't easily find a Wi-Fi hot spot to go to the church web site. (It's quicker with the app anyway, as long as you update the data on a regular basis... which is really easy.) To help with my calling, I used the "PDF Printer" on our MLS computer to create a few documents like "Members with Callings" and "Members without Callings" to keep in the iBooks app and have ready to review when needed. I also made electronic copies of things like the Home Teaching Reports just for reference. I suppose that makes my iPad a bit of a risk containing such confidential information but, to me, it's no less secure than having paper print-outs in a folder that I might carry on Sundays.
There's always a little frustration in Priesthood meeting when someone says, for example, "Let's read the second paragraph on page 85 of the Gospel Principles manual." Of course, the version in the app doesn't have page numbers. BUT I downloaded the PDF version of the Gospel Principles book and I can follow along there if I want to. It has exactly the same layout as the book and each page is about the same size as the paper version when viewed on the iPad screen. It lacks the hyperlinks to the scriptures this way but, with app switching, I can have the Gospel Library version ready too while the lesson is happening. Just double-click on the "home" button and you'll be all set.
I have no experience with other tablet computers. But, of course, I like the iPad so much that I don't think I need to worry about other tablets anyway.
My real name is Greg Anderson.