Explanation

For a small, long/short equity hedge fund open to new investment, the HFRX Index is the most appropriate benchmark because:

• HFRX (Hedge Fund Research Investable) Index consists of hedge funds that are open to new investment and have investable capacity, making it suitable for benchmarking funds that are currently accepting new capital
• HFRI (Hedge Fund Research Index) is a broader, non-investable index that includes both open and closed funds, making it less representative for funds seeking new investment
• Credit Suisse Hedge Fund Index is also a broad hedge fund index that may include funds not currently open to new investment

Since the question specifies the fund is "open to new investment," the investable HFRX Index provides the most relevant comparison for performance evaluation and benchmarking purposes.