If you ask 100 people the same question you’ll get 101 different answers. I prefer a V shape because the V shape flute can be very aggressive when roughing especially on green wood. When you need to remove a lot of stock when roughing a bowl or turning a hat where 99% of the blank ends up as shavings the V shape is the only way to go. The small nose radius is not grabby when entering a cut and can be used to create details. Because the wings tend to be longer on a V shape tool scraping is easily done on the outside of a bowl. In the past a V shape flute was known to clog with shavings, the design of this flute was changed so it doesn’t happen. The U shape flute is a traditional push cut style and has some strong points especially when turning dry wood. The large nose radius allows the tool to shear the wood which is good to prevent tear out, the finish cut inside a bowl, platters and some spindle turning are a few examples where this tool excels.