Visa applicants are generally supposed to apply to the consulate that has jurisdiction over their place of residence. You should therefore apply in the US.
India has outsourced its visa processing in the US to a private company. The website is https://www.in.ckgs.us/.
When visa duration varies, it generally depends on the applicant's nationality, not on the place where the application was submitted or the visa issued.
You may want to consider whether an e-Visa would suit your needs. This was formerly called the e-Tourist Visa; its current name reflects the fact that it also serves travelers who visit India for a "casual business visit." For more information: https://indianvisaonline.gov.in/evisa/tvoa.html.