A good painter will make either look smooth and well covered. Spray vs brush is a matter of preference.

New or repaint?

Just the siding or siding and trim?

What colors?

It's far easier to apply a sufficient amount of paint via spray. Once everything is masked, the second coat is as easy as the first.

For new Hardie, I'll spray a coat of primer on the entire house (body and trim if the trim is getting painted), spray the 1st coat, caulk, then spray the 2nd coat.

Then brush most or all of the trim.

As Millman says, level of experience and work ethic trumps all. Your question is old as the first applications of products to enhance appearance and longevity of construction materials. Rely on reputation of painter , not "I heards and They saids" online.

Repaint

PAINTING JAMES HARDIE ® SIDING AND TRIM PRODUCTS WITH COLORPLUS® TECHNOLOGY

When repainting ColorPlus products, James Hardie recommends the following regarding surface preparation and topcoat application:

• Ensure the surface is clean, dry, and free of any dust, dirt, or mildew
• Repriming is normally not necessary
• 100% acrylic topcoats are recommended
• DO NOT use stain, oil/alkyd base paint, or powder coating on James Hardie® Products.
• Apply finish coat in accordance with paint manufacturers written instructions regarding coverage, application methods, and application temperature
• DO NOT caulk nail heads when using ColorPlus products, refer to the ColorPlus touch-up section

-- HZ10 Best Practice Guide - Hardie Plank

Can i ask uou all a question my new construction house hardie looks like this after paint the one side is especialy bad looks like its a 1980s house is this normal?? how do we fix this?

looks like what?

Am I unable to see a picture?