It kinda all depends on what you will be doing, and how much money you have. I don't think there's any doubt that you can't go too wrong with the Festool products, but as others are showing, there are alternatives to what Festool has, and more.
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Here is a collection of ones I have bought or built. They all have their function.
Clamping Element
With a block of wood to attach to the end of a quick clamp and a bench dog in the jaw I turned a common clamp into a horizontal clamping element.
Love my Armor/Craftsman/Rockler horizontal clamp. it does not have the flatness of the Festool one, but it works for what I need it for. For flatness I go back my quick clamp and adjust the hold off at the end of the clamp.
End Stop
My HF stops from the portable work station fit perfectly on my MFT/3.
Not shown - Home made clamp stops I turned a dowel down to 20mm and then drilled some holes out of some plywood. Instant end stops built to order.
Take that idea and also made some cam claps as well.
Vertical Clamp
One gotta have, the small Festool F stye clamp, fits holes and rails. I use these clamps on just about everything I'm doing.
I created an interface for my Kreg clamps, They work great for holding something vertical. Take the T flange bolt out, flip it and the clamp to the other side of each other, and now they fit in the edge rail as well. Very easy to do. Used a 5/16" post screw down the middle of the dowel to hold the knob on.
By taking the nub off the end of my HF F style clamp, and hot meting a piece of plywood to the top jaw (keeps the leg from racking in the dog hole) , I use my HF F style clamp to hold things down on the bench when needed.
Rail Clamps
i have the screw clamps as shown, plus a set of DeWalt rail quick clamps as well. Use those for clamping rails for long cuts that are beyond the ability of my mft/3 to handle (Cutting down sheet goods).
You are only limited to your own creativity.
Enjoy.