We do formal or...
Allow your Groomsmen to invest in their own custom suit style including personalized linings to make the day even more special.
Perhaps the Groomsmen will rent their suits but the Groom wants his own custom made suit!
Rented suits and tuxedos may look uniform but never quite fit the way a custom suit will. Different suits and colors look amazing when the fit is right.
Consider buying each of your groomsmen a custom dress shirt?
Casual setting, casual look. Casual couples may prefer groomsmen wearing trousers and a vest.