Haven't experienced AF's biz but their food should be fairly good. Although dependent on when you're going LH will be using their 747-8 from LAX to FRA. You may be able to experience their new biz class (completely lie flat) which is far superior than their legacy product; but only above average in comparison to other airlines (i.e. SQ's biz product).

For me, I would go the LH route just because I'm a Star Alliance mile hoarder.