It all depends on whether you like sliced bread
As for the "round" aperture opening. Here is a general breakdown:
- The greater the number of blades, the rounder the opening
- Large number of blades are sort of incompatible with auto-aperture (lens stops down automatically at exposure time), particularly if high exposure rates are part of the design objective
- Many preset and fully manual aperture lenses have high blade counts and essentially round aperture
- Curved blades help when the blade count is low
- Shorter focal length lenses, especially vintage primes, tend to have lower blade counts. For example, my S-M-C Takumar 28/3.5 and Tamron 28/2.5 both have only 5 straight blades.
Now, to put things in perspective...
- The professional quality lenses for my view camera only have five straight aperture blades
- Even high acclaimed optics may have low blade counts. For example, the 35/2.8 Zuiko on my Olympus XA only has two! (Yes, the aperture is square.)
- Round or regular plane figures are not the only options. Some of my FSU rangefinder lenses have a fun-looking curved pincushion look to them.
Finally...
If you truly want round, SHOOT WIDE OPEN!
Steve