I have personally used ArcPad several years ago when I was a GIS student and it is definitely good for basic GIS personnel.
ArcGIS Mobile was meant to be used by people with no GIS experience because the out-of-the-box-solution provides a simple and easy to use interface for data collection. Depending on what equipment you are using this will require some hardware setup, for example if you are using a laptop and an external GPS, your employees will need to know how to setup a GPS to work with ArcGIS Mobile.
When I first embarked on my project the hardest thing for me to figure out was the GPS.
The greatest feature of ArcGIS Mobile is that you can code you own extensions to make workflows that meet your business requirements. For example I am using the out-of-the-box-solution but I coded my own data collection functions and I got rid of the ESRI's Data Collection feature.
If you are a programmer and have a lot of time, you can create something really impressive, but it is tough.
I do not have any experience with Collector but I am quite interested in it when it becomes more mature.
Regards,
Akhil P.