[tstyle]

The center vent looks more casual. It's associated with classic, Ivy League suits from the East Coast in the states and the actitivies that are a part of that (hunting, polo, etc.). It's not a hard and fast rule, but the history does give it a more casual appearance - and a sport coat is more casual than a suit coat. All too often a double vent on a blazer can look like you're wearing your suit jacket as a sportcoat instead of an item that's specifically made as such.