Hello Mohammed, I've been using a Mac Mini for OS X and iOS development now for over 2 years: I've had no problems that have been related to the hardware (as opposed to versions of XCode, OS X etc). Because I also use it for photo editing large raw files, I bought the higher spec model with an SSD drive and 8GB RAM. I think the SSD and RAM help with development tasks, especially where I have a lot of views and code.
I also use a MacBook Pro 13" with SSD and 4GB RAM for development and it's also fine, although a bit slower than the Mac Mini.
I have a 30" monitor (primarily for photography) on the Mac Mini and that really helps with large, complex storyboards (e.g. several view controllers and segues).
Regards.