Totally agree.

I had a 2 Sora/Tiagra bikes and outside initial set-ups,
I had no problems with either drivetrain.

My next group will definitely be a 105 5700 group.
Right now, I can't wait to get my hands on a new 5700 group.
I'm just waiting for it to go on sale over the winter as it undoubtedly will.
Then I'll snatch a set up for a wicked price and have it waiting for a bike to go on.

While many reasonably believe that 105 offers the best bang for the buck,
for me personally, I'd have to say that Ultegra is the value leader for the group.
It is undeniably better than 105 and undeniably close to Dura Ace.
But I'd want 105 for a budget build.

It's about 1/2 of what Dura Ace goes for and generally goes for "only" 25% more than 105.
While 105 "could" be raced, Ultegra can definitely be raced.
I consider Ultegra "Dura Ace Light".

Either way, just about anything Shimano makes is great.