By the polls the EC is 216-219 with 8 steps up for grabs to varying degrees. Harris’ VP pick needs to be whoever increases her odds of capturing 54 more EV the most. From the folks mentioned:
Kelly:
pluses: could be the deciding factor in AZ. Very high Q score who could help with suburbanites and/or never Trumpers.
minuses: boring. Unlikely to bring out young people or minorities, whose turnout will likely decide the election.
Shapiro:
pluses: could be the deciding factor in PA. Very intelligent, effective politician. Young.
minuses: could turn off pro-Palestinians. Unlikely to sway suburbanites. Unknown how he would impact young voters and minorities.
Walz:
pluses: probably locks down MN. Very effective politician. Folksy guy who will appeal to midwesterners (MN, MI, WI, rural/western PA).
minuses: might seem old. Harris can probably win MN without him on the ticket. Unlikely to motivate young voters and minorities.
Beshear:
pluses: Young, high Q score, knows how to appeal to voters as a blue candidate in a red state, so could help in AZ, NC, WI, and GA. Effective politician.
minuses: doesn’t guarantee a swing state. Not sure a white dude from Kentucky is going to help drive blacks in Atlanta or latinos in AZ to the polls.