It should match the rest of the pulls / knobs in your kitchen.

I wondered about this myself and ended up going with about a 6" cup pull from Restoration Hardware that matches my other 4" cup pulls around the room. I think it looks right and I think I like having a little more grasping room on the DW as it takes a little oomph to pull it open.

What brand of dishwasher are you purchasing? There's about 3/4" at the top inside of my Bosch panel above the controls, so depending on our model you might just be able to fit it onto the panel wood above the dishwasher door itself. But that's without considering the issue of having the pull so high on the panel -- will it be structurally sound there? Or will it pull the panel away from the dishwasher over time? That would be my fear - that it puts all the torque on the top stile of the panel, leading to damage...? This might not be such an issue with a slab door design.

Most of this is personal choice/preference. There are no hard and fast rules. Do you like the look of two pulls/drawer on wider drawers? If so, you could get all one size and put one on drawers less than, say, 30" and two on any 30" or wider. You usually do not have to worry about pulling a drawer unevenly with two pulls. As long has you have good quality drawer hardware, you shouldn't have any problems. We put knobs on doors and our 6" pullouts and pulls on all other pullouts and all drawers. In our case, we put one on drawers = 30". I think the 2-pull look looks more like fine furniture, and I happen to like the look. If I had it to do over, I think I might have put two pulls on the 27" drawers... As to the 6" pullouts, our pulls (5") were too wide to fit horizontally and I don't like the look of vertical pulls, so we went with knobs. We store heavy pots & pans and heavy glass dishes in many of the two-pull drawers. I usually use just one hand/pull to open drawers and have not yet hand any issues. If you prefer one pull/drawer, then most will look fine on the drawer widths you listed; none are that wide. I suggest picking a medium-sized pull and just using the same size. You can drive yourself crazy scouring the net and stores looking for the same pull in various sizes. Whatever you choose, I suggest only purchasing two or three of them and them mocking them up on your drawers to see (1) which look you prefer, (2) how you want to place them, and (3) whether they fit your hands and/or fingers (i.e., comfort). We ended up with two different manufacturers for our knobs & pulls (both birdcage in antique iron) b/c the knobs in one (Dec Har) fit our hands better (the stem was a little longer) and the pulls in the other (Siro) had nicer curves. Bottom line....what looks are you drawn to? That will tell you how you should place your hardware. I do have a pic of how I placed my knobs... As to our pulls, we centered them on the drawers fronts, except the trash pullout. The pull on the trash pullout is on the frame. Some pics of drawers of similar size to yours: 24", one pull per drawer: 27", one pull per drawer 30" drawers, two pulls per drawer (6" pullout w/knob on the right) 31" drawer (1), two pulls per drawer (another 6" pullout w/knob on the left) 33", two pulls per drawer (18" trash pullout to the right)