The Boss ML-2 is a more versatile pedal, offering a wider range of distortion sounds than the TS9. It has four different distortion modes, from a mild overdrive to a heavy distortion. The ML-2 also has a built-in EQ, which allows you to shape the tone of your distortion.
The Ibanez TS9 is a more classic distortion pedal, known for its warm, tube-like sound. It is not as versatile as the ML-2, but it can still produce a variety of distortion sounds. The TS9 is also known for its ability to boost the mids, which can help your guitar cut through the mix.
Ultimately, the best pedal for you will depend on your personal preferences and playing style. If you are looking for a versatile pedal that can produce a wide range of distortion sounds, the Boss ML-2 is a great option. If you are looking for a more classic distortion pedal with a warm, tube-like sound, the Ibanez TS9 is a great choice.