For me: 1. Tone (does the instrument help my tone?) 2. Is the horn open and easy to play? 3. Are the valves fast? 4. How well can it handle dynamics? 5 (This is a very personal preference of mine) Does the instrument have a 1st slide trigger? Ever since buying my Silver Flair, that has become a deciding factor for me. It's not as important as the others, but it's something I really prefer.