It really jusyt comes down to personal preference. 6 of one...half a dozen of the other. 105 and Ultegra are bioth nice and work great. Both frames will do the exact same things..... Just pick which one you like best- In the real world, you won't notice any real difference between 'em. The titanium frame may be more durable in the long-term.

One thing that might sway me towards the aluminum bike: It has a much better crankset (Shimano 6800) than the titanium bike. I've heard bad things about the FSA Gossamer cranks on the ti. -and I'm not prejudiced against FSA, as I have 2 FSA cranksets, myself...but not Gossamers.....