I also favor Clecos. I bought 50 and pliers from Aircraft Spruce. That was about the right number for me and they worked great. Try fitting even one pannel with sheet metal screws. After about the third time you've had the panel mounted and unmounted with several or a dozen attachment points, then tell us about the screws.
One other thing to keep in mind is that clecos will pull the panel tight to the frame (or other panel) without damaging the hole on either side. If you intend to use rivets (everyone does, right?) the sheet metal screws will bugger the holes so you will have to re-drill them before riveting. Screws just seem like a real effort in futility.
Lastly, shop around. Prices vary and since you buy a lot of them, the difference can add up quick.
John