I tend to agree with the majority here..  It depends on overall proportion.

I wish I were smaller all over, but that will never happen, as I have a very muscular build.  Even when I was a slim and slender teenager the stupid BMI told me I was overweight....  And I have now DD cups.  I don't have back troubles, because I have so much muscle there from swimming, but nor am I disproportionate - I'm stocky in build.

In my case, smaller boobs would make me look fat (ter).

On that note, my sister-in-law is so tiny all over she looks like she's got bird bones, and larger breasts would look SO wrong on her.  It's totally about proportions.

And underwires CAN be totally uncomfortable, depending on the shape of bra.  I had to try TONS of different shapes before I found some that didn't cut into my skin really badly...  You can get lots of no-underwires here in Canada though.  Maybe you should come shopping above the border, Susie!