For me, it would depend on what you do in a woodworking sense coupled with what you already have.
My first and second Festool Purchases were the DF500 closely followed by the DF700XL they have revolutionised my joint work, providing I cut straight and true boards, no issues with jointing.
I have a nice 10" cabinet saw, 3x various Circular Saws, a Radial Arm saw and a Sliding Compound Mitre saw, and 5 different Routers, my next Festool purchase will probably be a TS55 with some rails, although I am toying with buying a Kapex and losing the Radial Arm and Sliding Compound Mitre Saw.