First off, planing of a way to create a best table saw outfeed table is going to be based primarily on your workspace. For smaller workspaces, you may need to look at a small table, for larger spaces you can create a much more significant working table with other tools to help in your daily projects.
One thing to keep in mind is the mobility of the table. Do you plan on keeping it stationary, or would you like it to be movable or foldable? Are you going to need something that lets you push the outfeed straight along the table, or would you like to curve it so that you can move it to the side?
If you are building your own table saw, you have some ways to create an outfeed that goes with the table, but in most cases, you will likely be creating your own unique design that will fit with the table. In this case, you will want to try to create a flush outfeed table that will look natural with your table saw set up. Granted, this is for aesthetics for the most part, but you will notice that it actually makes it much easier to move around the workspace.
Plan in Details
A great idea is an outfeed that will work with your natural body movements. Think of it this way, as you are pushing the cut with your hands, once the cut is finished, where you would like the wood to move and with which hand is you leading. If you lead with your right hand, as I do, you want to be able to push the cut piece off to the right, as your arm naturally moves that way.
This leads to creating an L-shaped outfeed that will let you quickly move the piece to a large part of the outfeed table with one hand and very little movement outside of that. There is a problem though as it can be difficult to quickly move the wood if it is against another piece of wood. So proper materials are going to be key to ensuring that the pieces slide easily. I suggest laminate coating and if that isn’t smooth enough, make sure you give it a few coats of a sealer that will hold up well.
In addition, you may want to create small edges across the outfeed table to ensure the wood doesn’t fall off as you are moving it. The only issue is you are limiting yourself and the size of the cuts you make.
Finally, it is worth considering a quick storage option at the end of the table. Since most of my cuts are fairly thin cuts, when I need to use the table at least, I prefer a tall wooden “basket” for lack of a better term. The bottom of the basket has a bit of padding, and I added a naturally rounded slope to ensure that I can easily slide the wood into the basket. This is a simple design and can be made to be easily mobile, but I keep mine right where it is.