Dovetails: Should I make the tails on the front or on the sides?

You're making it put the tails where you think it looks best.

Dovetails are designed so that the tails help hold the piece together in the direction they will take the most outward stress. Look at a dovetailed drawer and the tails are on the side piece so that the tapers help hold it together when pulling and pushing on the drawer front.

Which way will have more stress pushing out with your tool trays? That's which side they would be on for a traditional look. Looking at your projects, to me that would mean tails on the end pieces.

Now, all that said, the design for strength was largely a result of needing the mechanical advantage with early glues that didn't hold as well. With modern glues, it's kind of a moot point. The wood will break long before the glue joint, so you can realistically put the tails on whichever side you think looks best and you aren't sacrificing hardly anything in strength. They would definitely be more visible and attractive on the side pieces.

Its a matter of taste.
I think the tails look best on the long side.

After all that work to make them, it is nice if you can see it when you open the drawer. If you are adding drawer fronts, you probably want them to show after they are completed.

Be creative, I have build drawers with no fronts and left ALL the joinery exposed!