My first device was the Mogul. I bought it about 2 weeks before the Touch came out. As soon as I layed my hands on the Touch, I gave the Mogul back and never missed the keyboard. If I am going to text more than a sentence or 2, I just call the person anyway.
I haave had my Diamond for about a month now and love it. It has plenty of storage for my needs. I have an iPod for music, an Archos for video, and a dvd player for TV out.
As for the installation of programs, I have done a hard reset(does not erase internal storage and can be done easily when powered off with 3 fingers) and did not let customization run. I then installed Opera PicMail, etc from the cabs in windows(installed them to internal storage). Most apps can be installed to internal storage and run fine.
The Pro sounds like a great phone also, but the Diamond works well for my needs.