battery life

Both those phones have the same raw battery power but they use it differently. The 9900 has about 20% more talk time, while the 9790 has about 40% longer standby time. So if you plan on talking a lot on the phone and need it to last longer throughout the day, then the 9900 might be your best bet. But if you plan on just having your phone around and potentially needing to use it, without regular charging, then the 9790 might be a better phone for you. Other potential factors are that the 9900 is faster and has a bigger screen, while the 9790 is lighter. Personally i'd go with the Blackberry Bold 9900.

This phone has the biggest battery around but the down side is that it is heavy