Bull nose is OK if it is appropriate for the age of the house and its style. I prefer a squared edge if the home predates bull nose, which is may 1970's or earlier. If either would be appropriate, I'd go for the squared edge, especially if the home is a retro style. Maybe I'm too old but I still see bull nose as being somewhat gimmicky. From a practicality standpoint, baseboard is much easier to apply to a square edge.

We just had this conversation with our new builder. 14 years ago, when buying our already under construction home, we had never heard of the rounded edge. We were given the option, and chose it. Loved it (and still do), especially with all of the detail that we have. Our trim joints have held up well and we have never had to re-caulk or even paint the trim. Our new builder says this is rare.

We have decided to go with the straight bead in our new build because of a few reasons:

The regular corner bead normally holds up better and doesn't dent as easily (miraculously, we only have one dent on rounded and one place where the edge is popping open.)

There is more work involved in creating the rounded bead. And more joints in the trim work. In other words, extra labor. That equals $$.

We just want a new look with more traditional corners. The rounded bead does make for fancy trim work!

Square and they also allow for changing colors easily from one space to another.

It's best to change colors at inside corners. It's very tricky to paint two different colors to an outside corner and have it look good. We have rounded corners in our house and love them.

Current house came with rounded, but not a choice I will make for the new house.

I personally love rounded corners, I think they look better than the squared off ones. I think it all comes down to preference though and either works great.

This is what we did to change the wall color in our dining room. The DR was the only room in the house completely opened to another area. The trim piece worked because we already had the trim on the end walls of the wainscoting.

I loved the rounded corners in my last craftsman house. My current house is transitional and square corners fit better. I would say it depends on the style of the house.