On-site is the highest-fidelity modality because presence preserves everything that carries meaning in a hard conversation: tone, hesitation, gesture, eye contact, and the shared physical context that lets an interpreter convey not just what was said but how it was meant. For sensitive and high-stakes encounters, those cues are load-bearing.
Within on-site work, the variables that drive a good match are language and dialect, specialty, credentials, and lead time. A $90/hour on-site Karen interpreter and a $120/hour on-site ASL interpreter are different products solving different problems. Getting the match right — the right language, the right specialty, the right credential level — is what makes the encounter work.