I have three-drawer stacks. I did the top drawer as slabs because I didn't like how skinny the top panel felt with a pull inside that skinny space. It also was a more interesting look, in my opinion. I don't know if there is a convention, but that is why I did what I did.

Here is a link that might be useful:

The reason for the top drawer usually being a slab, is that it is too short height-wise to do a five piece stile and rail construction.

blue devil I like your drawers. I also like the top drawer to be slab. I'm undecided about middle drawer(s) though particularly in a 4 drawer stack.

I have slab drawer fronts over my shaker cabs. My island has a rangetop with 2 wide 5 piece drawer fronts below it, and on either side of this I have a bank of 3 drawers--top slab, bottom 2-5 piece. I chose this to tie together in my slab drawer fronts. If I had everything having a 5 piece on the island, I feel it would look separate. Plus, having a slab up top draws your attention to the 5 piece for being different....I think .

You made me go look at my drawers! Look what I found:

What I'd never noticed before is that the drawer unit on the right has 3 slab drawers and the bottom one is a 5-piece. Although they look the same at first glance, the bottom one is actually about 4" taller than the other three.

I went with the 5 piece drawers everywhere. I recall the cabinet place asking which I wanted, and they said it was a matter of taste. One thing they mentioned was where the handle would go. Some styles leave only a very thin area in the center and its hard to fit the knob or pull there. My cabinets are shaker style and the 5 piece looked fine.

Conventional Shaker style is 5 piece for any drawer 8" or more. I followed that and it simplified everything.