help with road/commuter bike
New here an looking for some help. This year I started mountain biking and got a Gary Fisher Piranha. I want to start road riding with a friend and also maybe start commuting. My choices of bikes are Trek and Gary Fisher. I was thinking of a Trek FX 7.5 or 7.6. These are upright road bikes. My other choice is a Trek 1 series, which has the bent over more aggressive "stance". Being new to biking what are the benefits/ draw backs of each style of riding? I am 6'2" and 260 lb. and I have a compressed disk that gives my back fits from time to time.
I have a Trek FX7.2 and a Trek 2.1. I commute 18 miles a day. The 2.1 is my bike of choice. The road bike is slightly more aggressive than the FX7.2, but a lot more relaxed than other comparable entry level road bikes.