Go for a small cap fund if it suits your risk profile. This may sound cliched but many small cap funds have not given positive returns over a 10 year time frame; the small cap index hasn’t either. Find your risk profile using this tool.
Having said that both have done well. HDFC Small cap fund is much larger and has a better performance track record. SBI small cap fund is smaller and ranks lower.
Remember the two golden rules of mutual fund investing:
1. Invest for the long term by saving atleast 10% of your income
2. Invest only in direct plans as they can fetch you upto 40% more by cutting out broker commissions.