Compare multiple file suffixes containing date & time and do action on most recent

You can just do:

set -- logA.log."$(date +%m%d%Y)".*
eval "latest=${$#}"

(or shift "$(($# - 1))"; latest=$1 if you have religious objections to using eval, though that particular use of eval is perfectly safe).

As glob expansions are sorted lexically, given your HHMMSS format, the last one in that list will be the latest one.

With zsh:

(){latest=$argv[-1];} logA.log.${(%):-%D{%m%d%Y}}.*

Or:

(){latest=$1;} logA.log.${(%):-%D{%m%d%Y}}.*([-1])

${(%):-%D{%m%d%Y}} uses the % parameter expansion flag to expands %D{%m%d%Y} as prompt expansion. You could of course replace it with "$(date +%m%d%Y)" to make it more legible though that would involve forking an extra process and executing a separate utility.

Alternatively you could use zsh's builtin strftime command (in the zsh/datetime module) as strftime -s today %m%d%Y to fill the $today variable with that timestamp.

some_command_that_takes_this_file_as_argument $(find . -iname "logA.log.$(date +%m%d%Y).[0-9]*" 2> /dev/null | sort -n | tail -1) should do the trick

Edit: If you just want to use the newest logfile you could make it even easier:
some_command_that_takes_this_file_as_argument $(ls -rt | grep ^logA.log. | tail -1)