There is no one correct answer. Like most questions of this type, it depends on what purpose you are breaking down a sheet of plywood for. If you are getting into serious woodworking, such as cabinet or furniture making, no homemade jig or even one of the cheaper track saws will give you the results you will be happy with. For that you should be looking at the Festool (if money is no option) with the Makita and DeWalt vying for second place ( at the time I last researched the tool). I was trying to decide between those three when a close friend bought the Festool, which he gladly lets me borrow when needed. It makes clamping wooden straightedges like I used to to seem like using flint tools.
But if you are mainly looking to accomplish tasks such as cutting sheet goods for layouts or other instances when precision or appearance are not as critical then one of the options above will suffice. Some guys do just love building jigs and get carried away with them when reasonably priced commercial alternatives exist. I built my own crosscutting sled for my tablesaw that works great for smaller plywood pieces. It's really just your choice.
In the end, you'd be nuts to listen to guys you don't know (including me!) when considering spending good money on a tool. There are countless woodworking forums online where the specific tools are discussed and a consensus can sometimes be seen, as well as review sites and YouTube videos where you can see these things in action.
