I personally use VB, but it depends on what you're looking for.
VB has high liquidity and low fees, which is great. However it's not actually strictly small cap, and holds quite a few mid caps as well. This keeps the capital gains down, as it does not necessarily sell a company the moment it grows out of the small cap category. I also like how it complements a total market fund like VTI, which also holds a decent number of mid caps. Mix them together, and you get balanced exposure to large, mid, and small without needing a separate mid cap fund.
If you're not married to Vanguard funds, FSSPX, SCHA, IJR, and SLY are also good alternatives.