I use SplashID and like it very much. If you want to sync to the desktop, be aware that the companion application costs another $20, unless you already have a registration for a different version - then the desktop is free.
I've used SplashID since my early Palm days, so it was natural to move to it when I switched to the iPhone. It has improved with revision since it first came out for iPhone. Do know that there is a delay while it loads that some folks find annoying. It doesn't seem longer to me than many other apps. The most recent version allows you to attach images and documents to records, a very handy addition.