San Francisco is much better for running text than Helvetica. Lucida Grande is much better for running text than Helvetica. Verdana is much better for running text than Helvetica. Pretty much anything is better for running text than Helvetica.

Helvetica is a typeface designed for signage, headings, posters, corporate logos, and the like. For body copy, it’s terrible, because it has a strong boxy/griddy quality to it, many similar looking letters, and proportions which make letter shapes hard to see at small sizes.