The 7290 screen is MUCH better. When outside the 7100 gets washed out and then you can't see anything.
It really depends on what you want to do with the device. The 7100 is primarily a phone that you can read data on. The 7290 is primarily a data device that also has a phone.
I have a 7290 and love it, but I type on it way more than I talk on it. Since they both have BlueTooth, that is not an issue, but if you don't like the form factor for the 7290 you can always use a BT headset.
My recomendation is always the 7290!