I use an iPad and I love it. I also highly recommend the iPhone to most people.
While I love my Droid because it is much easier to type on than an iPhone, for most people I recommend iPhones.
Here are a few tips to make typing easier on your iPhone and your iPad.
1. Tap and Hold
When you press a key and hold it, you'll get additional options for that letter. This works for symbols too. Works great for delete (backspace) by making it delete much faster but you probably already know this. Bonus tip: Works with .com in safari to provide .org, .net. Pretty neat.
2. Tap and Slide
I hate having to switch between letters and numbers for only 1 number. So tap the number key and without lifting your finger slide it to the number you want. It's still 2 taps but easier than 3.
3. Tap and Hold Existing Text
When I first got the iPhone for my wife, I didn't know how to put my cursor in the middle of an existing (editable) word. Tap and hold in the word you want and you'll get a magnifying glass to move the cursor around.
4. Tap and Hold to Copy
Whether a link, a photo or a phone number. Tap and hold on things to get a chance to copy it to the clipboard.
5. Deleting Apps
Tap and hold an app and they start to wiggle and jiggle. You can then click X to delete them.
6. Pressing and holding the power button will completely power your phone down.
7. Press the power button and the home button at the same time and quickly let go and it will add a photo of whatever is on your screen to your photos.
8. Press and hold both the power button and the home button to force a restart.
9. Double click the home button and swipe through open applications. Swipe to the left and you can control your iTunes as well as lock the rotation.
10. Press and hold your home button (iPhone 4s) to activate Siri.