TOEFL and IELTS are both standardized test and used as a measurement for English language proficiency.Do the universities have any particular preference in case of admission (MS/Ph.D) of international students?
In most cases, there is no preference. The vast majority of graduate programs in the US accept both IELTS and TOEFL.
A program that does have a preference will say so in its admission instructions. For example, BU engineering prefers TOEFL:
In addition to the required credentials for applications, international students must demonstrate an understanding of English, including the ability to read and write with ease. International students are required to submit scores from or the Test of English as a Foreign Language (TOEFL) that meet our minimum requirements. If the TOEFL is not available, we will accept scores from the International English Language Testing System (IELTS).
If your first language is not English, you will need to submit an IELTS test score. Please note: this department does not accept TOEFL scores under any circumstances.
While Stanford only accepts TOEFL:
Stanford does not accept IELTS scores.
(While through Spring 2016 NYU GSAS acccepted TOEFL only, as of Fall 2016 they appear to have moved to the "no preference" camp.)
and NYU Graduate School of Arts and Sciences only accepts TOEFL:--
Do you accept the IELTS instead of the TOEFL?
So you can check if the specific programs you are interested in have a preference.