Just to toss in some personal experience I was where you are maybe five years ago. I have had Sora, Ultegra, Dura Ace from Shimano and Apex, Force and Red from SRAM. I like SRAM because of the method of shifting, but that is just me.
My first new Road bike was a Jamis with Sora. Yes the Sora Shifts well and it is easy to use the thumb shifter. But mine was a 8 speed and the 10 speeds had a better selection of cassettes and I wanted a 10 speed. My next road bike was a frame up build and got a deal on a SRAM drive train and shifters. You need SRAM Derailleurs with SRAM shifters but you can use Shimano cranksets and cassettes. My Second frame up build was with SRAM Force and yes it was smoother or at least I thought is was. This last assembly is with Red and it is smoother than my Apex. If I were doing it again today I would get a 10 Speed Shimano Tiegra or better or any of the SRAM shifters. If you are concerned with how much a second upgrade is going to cost in the future then remember it is often easier to get a frame and move the parts over to it. Shimano 105 is a good group set and their brakes aren't bad. SRAM Apex works as well and if you get the mid reach derailleur your choice of cassettes will go way up.
I agree with everyone else that the first road bike is only to teach you what you want in a road bike. But if you think you will have to live with that choice for a long time it is less expensive to get the parts you want on the bike if it is new. It is like buying a car, more than likely if you don't get the options you want you never will. (Just another point of view.)
