I think I go: 1A Tim Walz, 1B Josh Shapiro, 2 Mark Kelly, 3 Pete Buttigieg.
I love how down-to-earth, folksy, and relatable Walz is- I think it would help the Harris campaign enormously in the Rust Belt and the Blue Wall states. Plus, he seems to be getting genuine enjoyment out of calling the GOP out for their weirdness.
Shapiro is extremely popular and polls extraordinarily well in what I consider to be *the* most critical state that Harris has to win. I know there has been some unease on the left about how stances on Israel/Palestine.
I love Kelly's military and astronaut pedigree and think he would make the ticket even more palatable to centrist, white swing voters. Arizona would be a luxury to have in the EC, not an absolute necessity like PA and the other two Blue Wall states, and for that reason alone I've got him slotted 2nd after Walz/Shapiro.
I think that Buttigieg is outstanding in almost every way possible, especially with his ability to go into the lion's den on right wing media and effortlessly tie the weirdos in knots, but I think that he probably needs a bit more executive-level experience beyond mayor and Sec. of Transportation, which is why I have him slotted 3rd. I'd love to see him get an expanded role in a Harris administration, though. Perhaps Sec. of State?
All of that said, I really don't think that Kamala can go wrong at all with any of these four candidates.