Don't go with Sora! Seriously, if you can afford better, you will want to do so. Tiagra is acceptable. 105 is VERY acceptable and dependable and may be the best compromise between cost and performance. Ultegra is awesome and Dura Ace is exceptional!!! MOST of us do not need Dura-Ace (tho' we may covet it.) When price is a factor, get the best you can possibly afford. 105 will hold up smoothly for many, many miles. I had 105 components for over 30,000 miles, without changing anything but the chain and brake pads. Finally got a new bike and moved up to Ultegra. Could I tell the difference? I have to say, yes. Was it a HUGE difference? No. Noticeable, yes, because I ride so much that I am very sensitive to my ride. I can only imagine what Dura-Ace would be like. (Insert drool smilie here.) Point being, we make compromises between what we desire and what we can afford. Good luck in your choices.

annie