Go for one that is flexible, versatile (many options), available on multiple platforms and deals only in Direct Mutual Funds. Advisory support should be available if needed.
You can check Jama.co.in for these features as well (Disclosure: I work at Jamā).
Over here i have given 11 points on How to select the best SIP platform in direct mutual funds: Ram Medury's answer to What is the best site or app for investing in direct mutual funds through SIP?