Explanation

The Treynor ratio is the best measure when you are only concerned with systematic risk because:

• Treynor Ratio Formula: (Portfolio Return - Risk-Free Rate) / Beta
• It uses beta as the risk measure, which specifically captures systematic risk (market risk)
• It measures risk-adjusted returns relative to market risk only
• When comparing funds with different betas, the Treynor ratio properly accounts for their different levels of systematic risk exposure

Why not the others:

• Sharpe Ratio: Uses standard deviation (total risk), which includes both systematic and unsystematic risk
• Jensen's Alpha: Measures excess returns relative to CAPM, but doesn't directly rank funds based on their risk-return relationship
• Sortino Ratio: Similar to Sharpe but focuses on downside risk, still using total risk rather than just systematic risk

Since the question specifies being "only concerned with systematic risk" and mentions "different betas," the Treynor ratio is specifically designed for this purpose.