Table is far and away the best choice for T&G. If you do it hand held, it's really easy to slightly tip the router which messes up the tongue and/or groove. You can alleviate that by laying a second piece of your material parallel to the one you're cutting to support the router base.
Another thing would be an edge guide that will hold your router stable. Here's a picture of the Bosch unit, another of the DeWalt guide.
Another thing would be an edge guide that will hold your router stable. Here's a picture of the Bosch unit, another of the DeWalt guide.