Hello, I agree with the first answers and just want to add on: Some people (me) don't feel comfortable when others say, "Oh my God" or when they use profanity with "God". So instead of saying "God", please say "Oh my GOSH" to prevent drama or discomfort for others. :) It would be really sad to lose a friend or losing the chance to have a great friend just by not respecting (their belief).

Oh, my God, often written as Omigod, or OMG in texts, is very common and used by young people almost without thinking. Oh my Lord is more old fashioned.

First one is more common. I rarely hear the 2nd one