Advice on site structure

[allgenresaacq]

Im looking to restructure my site, If I have 4 different product ranges would I be best to either have

• 4 seperate sites under different domains
• Have my site set into sections such as www.mydomain.com/range1 - /range2 etc
• or have subdomains so www.range1.mydomain.com etc

Im thinking that I would prefer under 1 domain so as I dont have to promote 4 different sites. Is there any benefits to a certain method over another?