Sunflowers are heavy feeders and may compete for nutrients.  If planting in a vegetable garden, supplemental fertilizing is advised. Sunflowers are very beneficial to attract pollinators which is desirable.  A link to a companion planting guide for the vegetable garden provided by DUG (Denver Urban Gardens) follows.  It will provide many companion planting options to answer your question.  
https://dug.org/companion-planting/