Unless you want the groom to wear a particular colour or style its best left to him to decide
Like your fitting with the dress the groom might also have to have fittings and adjustments made. If it doesn’t fit properly it will show in the photos later.
The suite of the groomsmen normally looks different than the groom, You can choose to have slight variations with them. For example they wear different ties. Or They dont have a waistcoat to save cost and the Groom does.
Other Bridal party members
The groomsmen suite should all match. Otherwise it is hard to tell who is the groom in the picture years later.
If they are struggling to choose step in and tell them which one you would like them to wear