Black barathea is as Jock and others have pointed out is far too formal a look, if everyone else is wearing a suit, then wearing the black barathea would be far too formal. Wear the tweed, you will fit in with the other groomsmen. If it were me I'd wear something like this



or this


The colour of the tweed matters little, if you have a dark tweed, then wear it but if it's light that's fine as well.