i feel Big 4 audit is more value added with many non business people also know big 4 but when it comes to Marsh many don't know anything about this company. Marsh is quite good in accounting people mind but big 4 brand name is better and globally known. It would be easier for you to jump to other companies and field after doing few years and have better exit pathway. Good luck to applying big 4 and wish you could get the offer.