I am very familiar with Fuji bikes, and really am a fan of their products and how well they back them. My limited experience with Giant has me avoiding the brand, but mainly in the world of carbon fiber. I've just seen too many Giant carbon frames fail and they don't help the customer. Just saying. On the other hand, Fuji replaced a carbon frame for me just to be safe becasue the paint was falling off in suspect places.
Anyway, the Sportif is the better choice for long distance rides than the Roubaix. They are the aluminum versions of the Gran Fondo and Altamira respectively. The Sportif can be setup to be a little racier and the Roubaix can be setup to be a little more comfortable, just but doing simple things like flipping the stem and moving the seat fore/aft. Either way, make sure you get the right size (the LBS should at least be able to figure that out).
The main diff b/w Tiagra and 105 is, as another poster said, with the shifter. The Tiagra shifters are great for beginners since they have the gear indicators, but you quickly learn you do not need them. The hidden cable routing of the 105's alone make them worth the added cost. The group set component that differs the least is the front derailleur. In fact, there is little difference between the Tiagra FD and the top-line Dura-Ace FD, except the DA FD uses titanium hardware.
IMHO, for a brand newbie to road bikes, get the Sportif w/ 105 and ride it for at least a year and puts thousands of miles on it. During that time, make subtle adjustments to make it more aggressive, like lower the stem 5mm every few hundred miles, until you can ride comfortably with it all the way down and flipped down. Then next year, trade it in (sell it) for the Roubaix with Ultegra. You may even want to go carbon fiber by then
