Arun Sundaresan says that while expense ratio is important, investors should not overlook liquidity and impact cost, as they can significantly affect ETF returns. Higher volumes and liquidity result in lower impact cost. When considering portfolio placement, investors can choose from various types of ETFs, such as market cap based, sectoral, thematic, and niche strategies. The ETF market in India is growing rapidly and is expected to reach a significantly larger size in the future.