Either one, when set up and executed properly, can just as easily hit the ball DTL. Most people who can't effectively hit a DTL shot with their backhand blame it on an "inferior" 1 or 2 hand methodology. People that are envious of two-handers think the one hander is inferior, and vice versa.
OP: you should pick a methodology and stick with it. Learn how to execute it properly and it won't let you down. If you're having trouble hitting DTL with a 1HBH, then you're likely just doing it wrong.
But if your coach thinks you should learn the 2HBH, and you trust his judgement, then by all means: learn the 2HBH. But remember you're not doing that just so you can hit DTL. You're doing it because it's a fundamental mechanic that your coach believes should be adjusted.