The manual inversion, if done properly with chemistry kept in temperature and pH tolerances, will be more likely to not have scratches and/or dust in your film at the end of the day. Minilabs use rollers to pull the film through the chemicals. Rollers get dirty, attract particles, chemical encrustations, etc, as does open multi-gallon containers of chemistry kept at near 100 degrees F. Dip-n-dunk or hand-processing, while it won't completely prevent these things especially if the lab techs are not zealous in their maintenance and/or rigorous in their process, does greatly cut down on the possibility. I'd send each lab a test roll that doesn't matter to you and see which lab produces better results.